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".

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.

While the exact rules governing whether a death is heroic, just, or neither are not known (and indeed, there may be no exact rules), Andrew Hussie has explained that 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. On a side note, Hussie clarified that revenge-driven action is not disqualified from being heroic as far as judgement within the game is concerned, because that would simply be too big of a loophole to exploit.

's clock
keeps a grandfather clock, with a pendulum 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 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.

Just deaths

 * Vriska Serket died when 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 intervention having an unknown influence.
 * Jade Harley was 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 killed by Aranea, stabbed through the chest with a sword that had already skewered Jake, who had jumped in front of it in an attempt to save her. 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 removed the Ring of Life from her finger, immediately snapped her neck, and threw her into a wall of fire, where she faded back into a ghost. Despite the Condesce's status as a villain, the death was 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 fatally injuring Terezi.

Heroic deaths

 * Jake English sacrificed himself in an attempt to save Jane, by jumping in front of the sword Aranea was throwing at her. Such an act could only be parsed heroic.
 * Dave Strider was 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 mortally wounded by the Condesce after she attempted to avenge the death of Kanaya Maryam, and thus her death was judged heroic.

Trivia

 * Vriska HS 5751 (jokes) that if Tavros Nitram reached the god tier, 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.

Gallery
pics of dead kids here plox