Thanos snaps himself, reminds me of the pact spell.
Certain magic users use this spell to save themselves from death, even though sometimes it backfires horribly
Infernal is just cursed with basically Immortality until he kills Yuras and he is completely aware of it that it kills him but he does not care because he wants to join his dead wife and dead child.
Since Infernal is basically cursed to live until he killed Yuras, If he actually killed Yuras, they would die too by being reduced to ash or bones after a minute