I wonder what they'll do at the end of next season, as Sheldon will be finishing up his senior year at East Texas Tech, and does his graduate studies at Cal Tech when he's 14, so he should be headed off to California at the end of season 7.
Personally I'd be fine if they just ship him off and concentrate on the rest of the family, as they're more interesting, though George dies while he's at Cal Tech, so that will be coming up as well.
So would make sense to end it with him graduating and preparing to move off, mentioning in the voice over at the end that his father passes away soon while getting a goodbye hug from George.