Good question! I really don't know.
Tyson would probably have gone down in History as a better Heavyweight than what he will do but that said I think he would still have been beaten off Lennox which would probably have been his next fight. Also he would have never have bitten Holyfields ear and lost a lot of respect in the boxing world.

As for Holyfield I think he would still go down as a great but Tyson is definitley his greatest moment and without it he would lose a bit of the shine from his illustrious career.