I don't think he would have won. No matter what they thought of him at the time, they would have wanted someone else.
A good candidate might have beaten Reagan in '88. Dukakis was not a good candidate. Heck, he falls below the level of bad. He was actively bad.
What about Reagan vs. Lloyd Bentsen (flip the nominees on the Democrat, or perhaps Bentsen wouldn't have chosen Dukakis?)
Bentsen, I believe, would have been the only Democrat at the time that could have defeated Reagan for a third term. (He would have at least denied Reagan Texas and Bentsen might have taken a lot more of the south, of course he probably would have had chose a Mid-west or Northeastern Democrat for balance and to make sure of the win, a la the way LBJ did in 1964). Bentsen would have brought back all of the Reagan Democrats from the last two elections.
Of course California and most of the Far West (except for perhaps, Hawaii) would have stayed in Reagan's column, but they wouldn't have helped Reagan win re-election to a third term.
