I can't see that there would have been a replay, nor would the result been overturned if Croatia had scored.
Although rare this sort of muppetry isn't unprecedented, I can recall at least one other game a few years ago where a player was yellow-carded twice and played on for several minutes before the ref realised he should be off the pitch.
Also if you look at the outcome in terms purely in terms of the number of men on the pitch there's not a great deal of distinction between this situation and another in which a player should have been sent off but wasn't due to any other kind of mistake by the referee. In both cases there's a player on the pitch who shouldn't be there according to the rules of the game, but games aren't generally replayed in the latter circumstances.
Poll is a muppet and he's getting crucified in the press over here. I doubt the crowd at his first few Premier League games next season will let him forget it in a hurry either!
It does cast some of the comments earlier in this very thread regarding referees from the minor nations into a different light.