I think he MAY win one more Heisman, but I don't think he'll win more than that, and not because he'll leave college early. If he wins another, people will be so sick of his hype machine that they won't vote for him out of spite. I'll be surprised if he comes out early though, and if he does I think he'll be making a huge mistake. He's a great college player, but I don't think his style translates to the NFL very well, he'll get knocked for his size, and he doesn't really have the arm like Drew Brees and Russell Wilson do to overcome that size disadvantage, and those players both finished their eligibility and were not first round picks. I like watching him play, but I'll be disappointed if he doesn't play all four years.
There is something to that though and I think the Lebron example isn't great, one inch to a NBA forward is not that big of deal, two inches to a NFL quarterback can be, especially if you start at 6'0 or under. Guys like Drew Brees have proven that you don't have to have the prototypical size to be an elite quarterback, but if you don't think Brees would be even a slightly better quarterback if he were 6'2 or 6'3 with the same skill set, I don't know what to tell you.
You don't think guys like Kerry Wright or Issac Suber were two inches taller that they wouldn't have had a better shot at catching on in the league? Granted, I've only been a Blue Raider for a decade, but I think Kerry Wright has a legitimate argument as one of the most freakish athletes to ever play for MT. Had he been even 6'0, I think he'd still be in the league, but then had he been 6'0 I don't think he would have gotten more looks from bigger schools, so we would have never had him here.