In hell, no.
In the real world, well, yeah, they still got a shot. Shit can happen. Injuries, collective loss of focus (again), multiple players on the Heat catching fire all at once for a prolonged, multi-game stretch, hey, shit does happen, which is why they play the games.
But under normal circumstances, looking at everything objectively, you gotta think that this is still the Mavs series to lose, and that the events of Game 3 are not going to be a predictor of the rest of the series.