It's pretty rare for anyone to get equal value for a star that wants to leave. I was just saying what this whole situation would look like in other sports.
Musing aside, if there were swaps in real life and not just the papers then De Gea + Rafael for Carvajal makes a lot of sense. We get maybe the best possible RB signing in the entire world and they get De Gea and give Danilo the RB job but also get a talented (if oft-injured) backup who needs a new manager to replace him.
I'd be shocked if we get Carvajal, though. I assume he'll stay and fight for his job and they have no idea how Danilo will do anyways, so won't be eager to sell their young, Spanish starter. And if they do sell him, there have been Bayern rumours and he could just take Rafinha's job and play for Pep, so he'd probably do that.
I think it's the following, in terms of likelihood:
1 - De Gea signs for Madrid for about 20-25 million
2 - De Gea stays for a year and leaves on a Bosman
3 - De Gea decides to resign for us, surprisingly.
4 - We're closer to signing Bale than we think and we do a De Gea + 50 for Bale type deal.
5 - De Gea goes and we get someone else in return as full or part value. Illaramendi makes a fair amount of sense but he's been so unimpressive at Madrid that nobody is talking about it. Coentrao is rumored, and while that would be a poor use of resources, so was signing Falcao on loan when we had Rooney, Van Persie and Chicharito as 9s.