Death
A character will only die if the following 2 events happen: They fail all 3 death saving throws AND Nobody can revive them after combat
Succeeding on 3 death saving throws during combat will let you come back up with 1 HP ONCE, but suffer from temporary exhaustion. Once you go back down, it's as if you failed 3 death saves.
If you have failed 3 death saves, but are stabilized after, it takes a long rest before you are conscious again, even if some method would give you HP.