As has been said really depends what deal is signed at the time.
Mitch Mitchell died pretty much broke, he didn't earn a dime from royalties from Hendrix albums as he was a hired gun. That is the deal he negotiated at the time, I guess with hindsight!!
The reason U2 is a very rich AND a very happy band is because they have left nothing open to a 'what if' situation in the future. Everything and everyone is covered by contracts.
Pretty much from the off these guys have agreed everything is split four ways, pretty much five with McGuiness the Manager. So regardless who writes the song etc, four ways. As you said that is the reason they are still going.
Someone like Oasis fight like cat and dog because one entity of the band is earning four or five times what they are (Noel).......
This topic killed The Police. Copeland and Summers egos crushed the golden goose with Sting.
Mike Joyce (thinks that's his name) probably the best example. The drummer from The Smiths. He succesfully sued Marr and Morrissey in court several years back.
I wouldn't hold out much hope for Lib De Vitto, all he'll ensure is that he'll never play with Billy Joel again!!