I think Foreman would have won if Ali didn't rope-a-dope. He let big, foolish George smother his own punches. Had Foreman caught Ali with a punch at proper distance, Ali would have been toast. By leaning against the ropes and taking those body shots, he frustrated and tired Foreman. At that point in his career, Ali didn't have the legs/speed to dance the whole fight, but he could take the abuse to the body, especially because taking all those shots surviving was so frustrating to Foreman. Those shots were less damaging then shots he would have taking if George had given himself room to punch.

If Foreman had the same ring intellegence that he had in his comeback, he would have smoked Ali. The rope-a-dope was a genius move and it won Ali the fight.