No. Replays are basically recordings of the actions each player took within a match. You can watch from various viewpoints and change the flow of time, but you can't change the events that unfold.
The "what if…" question you ask is pretty difficult to accurately answer. If you had performed different actions in the match, your opponent may have reacted differently. For replays of multi-player matches that can't happen since you and your opponent are no longer connected. I suppose computer AIs could take over for the missing players - but then you're not really playing the same match.