Depends on the game and where their game saves are stored. Some games that use Games For Windows Live on PC require some extra files to be backed up (Like GTA 4...I am unable to use my old game saves because they didn't get backed up right on GFWL).
They could be under your Documents folder in My Games, My Game Saves, or in the AppData folder; just depends on the game.
If you wanna test it after you back up your data, install the game on another computer, copy the saves over, and see if you can at least load up the save, and then uninstall it from that PC.