>What services would have to shut down? How valuable is user data really? If user data isn't valuable, because advertising isn't valuable, then what else on the internet becomes impossible financially?

If it suddenly stops being the case that everything is judged against an ad-supported but free to use baseline, I think paid services become more viable than they currently are. There would probably need to be some work on payment models, but I think not many things would be forced to shut down (ignoring whatever shutters while the dust settles).