The practical side of me is of the opinion that, in the case where a member of a team is long gone, and there's a question about the use of their assets if the project winds up shutting down, everything should by default be up for grabs to whoever wants to use it themselves, provided proper credit is given. That's just me talking, though, and I realize that it kind of tramples on the rights of the original creator to determine how their work should have been used. In any case, I agree that setting up a definitive license is something that should probably be actively encouraged from here on out, and that some sort of licensing agreement should probably be a requirement for hosted projects, but I don't know that we should, or even can, go any further than that.