DND_Reborn
The High Aldwin
Name one (other than the DM/ table quitting that is...).You can have a situation with no PC deaths that results in an irreversible defeat for the PCs.
IMO there is always a story element that will allow the adventure to continue if the DM wants it to. Heck, thinking of it that way, even death doesn't need to be the end... the DM could have the PCs "adventure" in the outer planes (or wherever you have them end up...).