Right now, Nowitzki is planning to play through the pain, but he isn't ruling surgery out. But SB Nation's Mavs Moneyball outlines what would happen if the big man opted for surgery. Assuming arthroscopic knee surgery would take Nowitzki five weeks of recovery, the author says "nine games in an 82-game season isn't much."
Why nine games? Because Nowitzki could opt for surgery now and come back nine games into the season. Mavs Moneyball asks the question if surgery now is worth it:
Would you take a healthy, problem free Dirk and a 4-5 record, with 72 games to play in the season [if he has surgery] over a ticking time bomb and a 6-3 or 7-2 record [if he doesn't]? You would, and I would. But they haven't made that decision.
As the author points out, Nowitzki treated the same injury last season without surgery. But if a chronic problem can be fixed, it's an interesting question.