So just for a moment, let's pretend it WASN'T a fumble. Guess what? Utah still would have won.
Brian Blecken's hit was ruled a helmet-to-helmet personal foul. That would have been a fumble and Utah would have recovered it (no BYU players were anywhere near the hit). That drive ended in a BYU field goal. Without that, BYU would have been down 13-17, and would have needed a touchdown with 4 seconds left, not a field goal.
Eddie Wide was sprinting down the sideline and had one man to beat. He was tackled by the shoulderpads, AKA a horse collar tackle. No call there. That would have been a Utah touchdown, seeing as how there were no other defenders anywhere near Wide. That drive resulted in a field goal, but were it not for that BLOWN CALL, Utah would have been up 24-16 deep in the fourth.
Assuming that really was offensive pass interference in the end zone (which it wasn't), and assuming Utah didn't score on that drive, but also assuming the game was officiated correctly on both sides of the ball, the score would still have been 17-14, BYU ball with like 3 minutes remaining. We take away the "offensive pass interference" but add the Eddie Wide run for a would-have-been touchdown, so they cancel out. But Blecken's hit forced a fumble that wasn't, and led to a BYU field goal, which made it a 1-possession game rather than a 2.
So really, all things considered... Utah still would have won, because Harleen's not open anymore. No more last-second touchdown miracles for you. Only last-second blocking miracles for us. :)