This is not a problem that technology alone can solve. It neither is a problem unique to OpenID. Any third party provided identity have this “feature.”
XDI.org has been dealing with it for many years. Last year, several OpenID provider shut down its services. However, some classes of OpenIDs survived it. They were members of XDI.org, where they escrowed user data etc. so that the transition from one service to another for the user was possible.
I think the OpenID community should start thinking about this kind of infrastructure more seriously.