It's always a lava pit or acid pit. Why not something interesting like corrosive gas or simply being cut up too badly to survive?
Star Wars has always had a large multi-spot battle at the end (the famed "reel 6" for all the SW movies) So why not a three way battle between Yoda/Palpy, Mace/Dooku, and OB1/Anakin. Here's a good plot:
OB1, Ani, Maca and Yoda all come in to attack Palpy and Dooku. OB1 tries to order ani around, and the Emperor feeds Ani's anger until he turns on OB1 and attacks.
Mace and Dooku are fighting, and after some cool moves and force usage Dooku beats Mace, killing him.
At the same time, Palpy attacks Yoda first with the force. After the two deflect eachother a bit, Palpy pulls out his saber and attacks Yoda, and they begin a fight. After a bit more frog-hopping from yodaman, he is blown/knocked/pushed off of a cliff or ledge, depending on where they're fighting. Palpy thinks yoda's dead, but he survived, and leaves in disgrace.
Meanwhile, Ani and OB1 have been fighting, and Ani pushes OB1 into a wall knocking him out. Palpy tells Ani to complete his journey, and Ani slays Dooku easily. Then OB1 gets back up and Ani attacks, but OB1 wails on him. They eventually find their way to a pit containing some deadly substance you shouldn't fall into, and OB1 knocks Ani into it.
The final shots would have to do with OB1 getting to Tattooine and giving Luke to Owen, Yoda landing at Dagobah, and The very last shot would be Vaders helmet, with two Vader breaths, then credits.
Sounds good to me!