I think the more interesting question here is what they do with the code he has already contributed. They can, of course, try to remove it but I wonder to what

I think the more interesting question here is what they do with the code he has already contributed. They can, of course, try to remove it but I wonder to what extent a "bad actor" could claim that the replacement code was a derived work of their original code. I've always hated the practice of copyright assignment in projects, but it's things like this that make me wonder whether it is necessary after all.