It's a great thought. Everything really depends on game 5. If they pull that out, then it really is anyone's series, as the Celtics have the next game at home...and then anything can happen in a game 7.
However, 3-1 leads are hard to come back from, especially when you go out like you did in the finals last year. Was that really their best effort? If it was, then it is over and you have to tip your hats to the the [ghetto] Heat.