Dirk's fadeaway is unblockable. That's just a fact that comes with his size.
The trick with him is going to be to play hard, physical defense against the rest of his game. Get him to miss those shots and his psyche will be damaged, which will hopefully (if you're a heat fan) force him into a funk.
I don't really see it happening. The dude's been playing like he's on a mission the past 4 weeks and I expect it to continue.
But, basketball is a team sport. One person cannot win a series by himself (look at LeBron v. Orlando a few years ago. He scored 49, 35, 41, 44, 37, & 25 at 49% and they still lost). So assume Dirk is gonna get 25-40 every night (closer to 40 imo). The series is going to be defined by how Terry, Barea, and co. do. I think they're going to have a much tougher match up.
However, Dallas has been playing great D and Miami's O hasn't exactly been lighting the world on fire. So Dallas won't have to get too much from those guys to get Ws.
I don't have a clue who's going to win, but I'm leaning toward the Heat. That said, Dallas has a good defense and a decent O that can become unstoppable when Dirk is feeling it. That's a great recipe for success in a 7 game series.