The Bucks can't win the series, but if the Heat look past them they could manage to make it kind of tough for them though.
Mbah A Moute has the skills to guard LeBron as well as anybody else in the league.
They have the size inside to cause some problems for the Heat offensively and guard Bosh fairly well. (SANDERS, Ilysova Dalembert, Przybilla, Udoh)
And if Ellis, Jennings, Reddick and Dunleavy shoot the lights out, while the Heat struggle to knock down their shots, they could easily steal a few games.
I think its an exaggeration to say all of the Big 3 have to go down for the Bucks to actually have a chance to win. I think if any of them go down the Bucks would have a chance, not a good chance, but a chance. If Mbah A Moute can hold LeBron to human stats and Bosh goes down they could dominate inside, or if Wade goes down and the shoot well they could win.
Realistically though as long as the Heat have LeBron they will win. I just hope the Bucks find a way to steal a few before they do.