Conditional immortality

Conditional immortality is a term used to describe the rules governing the life and death of Sburb players who have ascended to the god tiers. The basic principles are first described by in HS 5530 (a conversation) with Rose Lalonde. He states that a god tier player is immortal, but that this immortality is conditional. A god tier player "will live forever, unless killed". When a god tier player is killed, they will revive unless their death is judged either "Heroic" or "Just".

The revival process is not instantaneous, but it is unclear exactly how long the delay is, whether it varies, or why there is a delay at all, given that the judgment appears to be made almost as soon as the death occurs.

In the A1 trolls' session, Meenah Peixes made intentional use of the delay to avert revival, by HS 6898 (killing all twelve players) right before the session was scratched. This was timed such that the god tier players among them (Meenah included) would not have time to revive before the scratch activated, thus allowing them to persist as ghosts in the dream bubbles rather than being erased with the session.

Judgment
The Heroic and Just judgments are defined "[b]roadly, mysteriously, and according to the case of the individual." Generally speaking, a Heroic death will result if the player was killed while opposing a corrupt adversary, or in an act of self-sacrifice for the greater good. By contrast, a Just death results if the individual is directly responsible for terrible actions, or if they have been subject to corruption by a villainous influence. stresses that these labels only apply to god tier players; when Rose asks him what sort of death he would have, he responds that he will not have either, as he is not a god.

The exact rules governing whether a death is Heroic, Just, or neither are not known, and Andrew Hussie has noted in a news post that he never intends to codify a complete list of rules. He does, however, indicate that they are closer to being hardcoded rules of the game than moral judgments, by pragmatic necessity in enforcing them.

On the subject of "close calls" in the judgment, Hussie remarks that:
 * There's reason to think there is a nuanced scale ranging from Heroic to Just inside the clock. There may be many shades of justice and heroism, some forms just barely qualifying to seal one's fate. But there's nothing nuanced about Alive vs. Dead. The result of a coin flip is absolute, even though there may be many subtle factors contributing to which side it lands on. Such as whether the coin is pure of heart, and whether the table it lands on has ever killed a man.

He then goes on to discuss some close calls, and what factors affected the results of those cases. In addition, he goes into detail on the difference between John Egbert's intent to avenge Dad and Mom's murders by Jack Noir (which was judged neutral), and Rose's intent to avenge Kanaya Maryam's disintegration by the Condesce (which was judged Heroic).

One of the determining factors for a Heroic death involves taking an actual step of action (no matter whether it succeeds) against such a corrupt adversary. Heroic intent alone isn't enough, which is why John's HS 5596 (death while fighting Jack Noir) didn't stick. Presumably, the same applies to earning a Just death: villainous action must be taken. Although it was HS 5530 (previously suggested) that a Just death must occur at the hands of a hero, the subsequent deaths of Jane Crocker and Aranea Serket, respectively killed by Aranea and the Condesce, proved this was not the case. Similarly, sacrificing one's own life to save an arguably villainous person can count as Heroic, as shown when Jake English sacrificed himself for Jane.

Hussie specifically clarifies that revenge-driven action is not disqualified from being judged as Heroic, as that would simply be too big of a loophole to exploit. This is because it would lead to any vengeful hero – which villains' atrocities have a habit of producing – being completely impossible to permakill as long as the villain remains alive.

Receiving mortal injuries under Heroic or Just conditions is enough to make the judgment count, even if the player survives for a short while before succumbing to them.

's clock
keeps a grandfather clock, with a pendulum HS 5751 (ticking between) the Heroic (in Prospit colors) and Just (in Derse colors) halves of the clock, while displaying the aspect symbol of the player in question. It is unclear if the clock simply displays the outcome, or if it has deeper ties to the resurrection of god tier players, but in the news post linked above, Hussie seems to imply the latter. In particular, there is uncertainty over whether Spades Slick's use of a juju breaker on the clock HS 5760 (while it was arbitrating) Vriska Serket's death had any influence on the result.

Known judgments
There have so far only been seven permanent deaths of god tier players shown in-comic. In addition, numerous doomed timeline ghosts of players have been seen as gods, but how they received their permanent deaths is still unknown. However it is possible that the cessation of their timelines is enough to ensure their deaths beyond the two normal criteria for permanent death, or that even remaining in the doomed timeline counts as Heroic, as it allows the alpha timeline to continue. However, in contrast to that, a doomed version of Calliope HS 8978 (eventually died) before becoming a ghost, rather than waiting for the timeline to fade away.

Neutral deaths
Otherwise appropriately termed "revivals", these deaths were neither Heroic nor Just, and thus the god tier player revived shortly afterwards.
 * John Egbert was HS 5596 (sucker stabbed) by Jack Noir while facing him down with Rose. Despite facing a villainous adversary, John did not have the chance to take any step of action. Therefore, the death was judged Neutral, and he HS 5753 (revived) a short while later.
 * Jake English was HS 8667 (killed) by Jane after his involuntary and impenetrable Hope aura dissipated. Due to a lack of any conscious action on his part, this death was judged as Neutral, and he HS 8704 (revived) shortly afterwards.

Just deaths

 * Vriska Serket died when HS 5737 (she was stabbed) by Terezi Pyrope. Terezi did this to prevent Vriska from accidentally tipping off Jack Noir to the trolls' location, which would have resulted in him killing all of them. According to the clock, Vriska's death was Just. However, Hussie stated that the ruling was meant to be ambiguous, due to Spades Slick's interference.
 * Jade Harley was HS 8550 (killed by Aranea.) When the clock was ticking, it very nearly stopped in the middle, but ultimately ruled the death as Just. This is due to Aranea manipulating the clock into a "Lucky 8r8k!!!!!!!!". Hussie explains that Jade's corruption was not typical mind control: rather, the Condesce had "turned off her ethical filter", allowing her to act on more evil impulses that she would normally suppress. This alone does not condemn her, as her behavior was still compromised, so the death would have been a close call, possibly sparing her. However, Aranea's luck allows close calls to break in her favor, ultimately being the deciding factor.
 * Jane Crocker was also HS 8801 (killed by Aranea,) who stabbed her through the chest with Brain Ghost Dirk's katana (with Jake impaled on it). Aside from the clock visual and Aranea's manipulation not being shown, the circumstances surrounding Jane's death were essentially the same as Jade's.
 * Aranea Serket died when the Condesce HS 8808 (removed) the Ring of Life from her finger, immediately HS 8809 (snapped her neck,) and threw her into a wall of fire, where she faded HS 8812 (back into a ghost.) Despite the Condesce's status as a villain, the death was HS 8814 (ruled as Just) because Aranea was committing a number of villainous actions: she intentionally doomed a timeline by essentially destroying the session, which she initially accomplished by corrupting Jake, whom she later killed along with Jane, as well as killing Jade and fatally injuring Terezi.

Heroic deaths

 * Jake English HS 8801 (sacrificed himself) in an attempt to save Jane, by jumping in front of the katana Aranea was throwing at her. Such an act could only be parsed Heroic.
 * Dave Strider was HS 8801 (killed) by Jack Noir and the Prospitian Monarch. Because he was facing them in an attempt to "save" Jade – although the two carapacians were not directly threatening her, they were obstructing Dave's intention of taking Jade's body back to Jane for revival – he died Heroically.
 * Rose Lalonde was HS 8801 (mortally wounded) by the Condesce after she attempted to avenge Kanaya's death, and thus HS 8881 (her subsequent death) was judged Heroic.

Related concepts
It has been implied that most if not all of the various forms of invulnerability or immortality offered by paradox space are fundamentally connected, though very few details on this subject have been explored so far in canon. When cherubs undergo their transformation for mating, they tap into their HS 7871 and become completely invulnerable to everything except one another. Aranea states that these forces, i.e. god tier players, , and his servants.

The power exhibited by mating cherubs, as well as and his servants' "clockwork majyyks", generally manifests in HS 5943 (the) HS 5969 (form) HS 7161 (of) HS 7721 (rapidly) HS 7732 (flashing) HS 7871 (colors.) 's clock also displays this effect when  HS 6011 (emerges from the excellent host,) and 's coat has the colours running around its edge. In addition, similar (but not identical) visuals are seen HS 5753 (when god tier players revive,) both on the players themselves and HS 5752 (on 's clock.)

Conditional mortality
HS 5969 (describes) the nature of 's curse on those who serve him as "conditional mortality", to contrast with conditional immortality. The terms of the curse are that his servant cannot die unless they do so in combat with the person has selected to replace them. In short, where conditional immortality has resurrection as the desired outcome, contingent on the judgment falling in the middle, conditional mortality has death as the desired outcome, contingent on completing service to.

Upon killing the existing servant, the new servant then inherits the curse. This has so far been seen HS 5971 (only) HS 5976 (once,) when the Condesce succeeded the Handmaid.

Unconditional immortality
Aranea describes as having HS 7897 This is part of the 'reward' Caliborn receives for choosing the path of the destroyer in the Choice offered to him by Yaldabaoth, the other part being

Inability to keep down the clown
HS 7384 (Clowns are notoriously difficult to kill for reasons that basically don't make any sense.) How related this phenomenon is to the above principles is unknown.

It's worth noting, however, that of all the clown themed characters in Homestuck (and other comics by Hussie), Gamzee Makara is the only one actually portrayed as difficult to kill.

Trivia

 * Vriska HS 5751 (jokes) that if Tavros Nitram reached the god tiers, he would be completely indestructible, implying that he's too lame to die a Heroic death or a Just one. However, during HS 7161 (this Flash), a god tier ghost Tavros was seen, meaning some version of him he must have died after achieving god tier.
 * Likewise, Nicolas Cage as a god tier will never die either,