Since the Memphis game I will say that the Lakers have played pretty well. They've won probably about 75% of their games when not playing on the second night of a back to back, with most of those losses coming to good teams on the road. That said, I'm not sure that D'Antoni had anything to do with it. He doesn't have Kobe's respect; he can't even stand up to Kobe enough to get Kobe to rest when he needs it.
At the start of the season the consensus was that the Lakers could be a title contender IF they were all healthy. Well, the only person even remotely close to healthy all year has been Kobe and the 7th and 8th players on their bench (Meeks and Jamison). I'm guessing that if the Lakers stayed healthy all year long (and that means Dwight being at 100%) they would be a top 4 team, battling with the Clippers, Denver, and Memphis. I think if the entire team came back healthy (again, Dwight getting an entire offseason to heal and train), they would be a top 4 team even dealing with injuries here and there (i.e. no season ending injuries).
That said I don't think D'Antoni is a championship coach. He's great for a small market team with limited funds, but he won't ever work in LA. I hope the front office recognizes this and moves on at the end of this season, but I'm guessing he'll be given another year unless Dwight and Kobe speak up.