Heh....the EU boys are gonna hop all over this one claiming he's still alive and whatnot...
but I say what happened was he was on the skiff with Han and Chewie who were trying to save Lando who'd fallen off, luke was on the OTHER skiff, and Boba was lining up a shot to kill him, when Chewie told han that boba fett was behind him, Han swung blindly, hit the emergency activation button on his jetpack
(what kind of pack has emergency activate, seriously?) Boba flew out of control into Jabba's barge, collapsed down into the pit of carkoon, and was eaten by the sarlacc.
Triple Dog Pass.