If after Roosevelt, the two term limit wasn't imposed, then who whould have ran again? And would this have changed political history? We know of course that Nixon toyed with the idea, and Bill Clinton has voiced support for an amendment, so Cliton (if he had been elected twice in the first place) would have given it another shot. I doubt Truman would have run, but would Eisenhower went for a third term against say Kennedy? And Reagan, would he have run?
You leave out the biggest blunder of presidential history by cutting it off with FDR (though I understand what you're doing). TR loved being president. He'd have wanted to do it until he died if given the chance-- and he'd have easily served two full terms in addition to his partial term. Alas, he announced that he would count the partial as a full term the night he won and regretted it every day thereafter. A very sad story.
