Why didnt Morrie just whack Jimmy to get his money back?
Morrie would have been better off tracking Jimmy down alone by himself having him killed or killing Jimmy himself, then robbing his house to get his share of the loot back, that way Henry or Tommy takes over in Jimmys place and the blame gets passed to someone else in Jimmys crew, like say Frankie Carbone or someone like that, either way Morrie would have gotten his money back.
But poor Morrie was too stupid to consider killing Jimmy in secret and taking his money back, Jimmy was not a made guy and thus his death would be viewed as a bad thing but not investigated, it wouldnt cause anyone to get whacked for doing it.