I'm sorry that you feel that way about the movie Mandy. From the accounts I read, he was very pleased to be working on the film. In the behind the scenes bit on the DVD, Heath felt very grateful to Gilliam and said he'd work for him for nothing. I also liked that those were his last words. They were funny. I'm sure Heath would have appreciated the irony considering his profession. And I'm sure he loved his last role. He was always wanting to have multi-faceted roles, to play complicated characters. And if you listen to most actors, they love playing villains because they're always more fun to play than the hero type. I'm sure that's what attracted Heath to the role in the first place.
If you like, watch Heath in Casanova again. Watch the very last scene. When I think of Heath, that's what I think of. Somewhere, someplace, he's with some traveling show, on a primitive side-show theatre stage, out in the beautiful countryside, with people he loves, doing what he loves, with the smells of fresh air and greasepaint in his nose.