Too many variables to make a meaningful prediction. Does Douglas actually put forth the effort to get back into necessary shape ? Or does he show up looking like he did against evander and grab his check and run? Does Tyson go out there and try to seek retribution with a vengeance or is he too emotionally scarred from the memory of the first meeting? I really don't know. But in all reality I think James was finished boxing or at least for the time being. His mental resolve for the game had diminished after being in the two biggest fights of his career back to back. He wasn't a man for the spotlights and nor did he seem to be money hungry.. Tyson on the other hand at least attempted to go on with his career. He hired rich Giachetti to replace his team, seemed to get some of his motivation back and had a few good fights before going to jail... I still won't make any convictions but Tyson seems the more logical pick..
Tyson would get his vengeance here. After the loss to Douglas he didn't go back to being the same old world beater, but he had some fire about him. Douglas in his very next fight with Evander Holyfield was back to being his usual unmotivated self. This is a good recipe for a big Tyson knockout, and he'd do it in quick fashion the way Evander did. Mike Tyson wins over Buster Douglas by a second round knockout.
I don't rate Tyson with anywhere near the acclaim many people give him. But in specifically 1991 I think Tyson scores a stoppage. I think Buster was disinterested and rich at that point.
The stars were aligned for Douglas to maximize his potential, afterwards he returned to his natural level.