When I first completed HoS I had no problem. I exited the game upon completion. When I got back on later I noticed the temple where the story ends was no longer there, just a giant hole in the map that I immediately fell through upon entering the game. So I tried reloading previous saves but that didn't help. When I reach the end of the cave where the temple is supposed to be there no longer is any temple, just a gaping hole in the map that I fall through forever. Reinstalling would be a nightmare at this point, do I have any other options?

Depends on the time between exit and re-entry as to how many updates have been added.

... The game has had major changes made to it. Do you want to play it, or not? Reinstalling is your only hope.