How is The Witcher not already in this discussion?
Well first of all, best of luck and I hope you come back safely.
Here are my thoughts for single player games that you can get loads of gameplay out of:
-far cry 2
-Stalker and Stalker Clear Sky
-The witcher enhanced edition
Those are mainly RPG games (like fallout 3) since I would think that if you've got lots of time to get through a bunch of single player games you'd want to play games that last a long time and have loads of stuff to get through.