Obviously, its tough to expect him to play the entire game. That would surely hurt his productivity in this game and the rest of the series.
However ... if I were Rick Carlisle, in addition to tinkering with his backup, I'd be asking my star to push himself to sit as little as possible. Because as Jeff Fogle of Hoopdata points out, the Mavericks have been better than the Heat almost whenever Nowitzki has been in the game. The Mavericks have been outscored by eight points in the three games combined, but almost none of that happened on Nowitzki's watch.
In the 124 minutes that he played, Dallas has outscored the Miami Heat by 23 points. As strong as Miami has looked earning a big riding time advantage through three games, they're WAY down when Dirk is on the floor.
Here's the breakdown in plus-minuses so far from the Dallas perspective:
Game 1: with Dirk -2, without Dirk -6
Game 2: with Dirk +13, without Dirk -11
Game 3: with Dirk +12, without Dirk -14
Because Nowitzki finishes every game unless he's fouled out, we've developed a pattern where the Mavericks fall behind during his rest time, then spend the fourth quarter trying to climb back to equality.
They successfully rallied to equality in Games 2 and 3, with coin-flip endings splitting out one apiece.