As an outsider to the Mavs, I don't watch Rick Carlisle every day so I can't say my opinion is 100% informed; however, I'm not sure how you can pin this on the coach.
The current Mavs unfortunately have a similar achilles heel as the Harden Rockets. If the center of the universe (Luka or Harden) is slightly off for any reason, the team has really no chance to win. I actually felt like the Rockets had the talent to developed a plan B, but Harden was simply too selfish. I don't think this is the case for the current Mavs and Luka. I think Luka would be happy to play off another player, I just don't think the Mavs have the talent to let anyone else run the show...or even dribble the basketball. I know KP is considered a "star", but he pretty much sucks in every situation. Luka makes him look like a useful NBA player, but if he played without a gifted play-maker he would be permanent hot garbage. I just don't see anyone on the Mavs roster that is good enough to consistently take the pressure off Luka.
Tough series, but I think you should hang on to Carlisle even if you lose in 6. He is a proven coach and I actually thought he did a fine job this year weathering injuries. If the GM would step up and find a legitimate #2 to run with Luka, the Mavs would be a very scary team. As it stands, if you can take out one man, you can beat the entire team. I highly doubt Carlisle wants to play like this...I just don't think he has a choice.