While I admit the Heat's chances of winning it all look very strong, anyone who thinks this series is over is delusional. If OKC can snag game 5 from Miami, they get to go home to their very strong home atmosphere in Oklahoma City.
Ya, winning three against Miami will be very tough...but we have seen plenty of comebacks in these playoffs (Den vs LAL with Denver winning 3 in a row, OKC vs SA with OKC winning 4 in a row, BOS vs MIA with Celtics taking 3 in a row). We are just going to have to wait and see how things play out.
EDIT: Wanted to add that my original prediction for this series was Miami in 7 (winning out due to their previous finals experience).