Tyson would beat the post-comeback Ali. That Ali would eventually get caught with a solid punch, and while probably not get knocked out, would be slowed even further, enough to lose a decision.
Pre-comeback Ali would beat Tyson with a boring jab-clench-dance decision. Ali would be too smart to trade with Tyson, and instead would opt for minimal engagements and stalling for time. It would be the most disappointing match ever.
In a "real fight" though, not MMA, I mean prison fight, Tyson beats anyone. :icon_twis