I'm not sure what is actually possible - or legal, even. LucasArts would probably not yield their greatest brainchild without attaching a contract that details what can be done with the characters and what not. The "Return to the original state" at the end of the series, which would enable LucasArts to continue the story easily in a 6th game without paying attention to the way TTG handled the characters, might have been the first point on the long list.
Guybrush will definitly get his hand back (
otherwise, it would have been no use hinting at the Vacaylian's ability to reattach limbs in chapter 2). It would be great having LeChuck remain both human and "good", but he's definitly up to something... chances are far greater that he will be G. P. again by the end of chapter 5. Or zombie. Or demon. Whatever!