I accidentally left my hard tribe on for twenty-four hours because I thought it was paused. Everyone died, but is it possible that any newcomers might still fall out of the waterfall? (I hope so! But I doubt it.)

Unfortunately, there must be at least one living adult villager to get an Island Event (like the waterfall or barrel o' babies). I'm sorry, but you will need to start a new game.

LadyCFII is right. You will have to start over again. Sorry!

That happened to me once.I had to start over.