Against an arbitrary future? No. Against a likely future? Yes.
It is not the hallmark of intelligence to come up with every possible thing that could go wrong and build defenses against it just in case someone somewhere does something counter to their wellbeing.
If you use any third-party login system, think about how you can migrate users between accounts, or validate that they are who they say they are, that's perfectly normal. What if Twitter OAuth goes down? What if your Google dev account is suspended by some automated system for some reason? You should definitely have some kind of plan for that.
Spinning off contingencies in case Apple changes its developer policies out from under you and suddenly no one on iOS can log in? Too specific and arbitrary.
It isn't?
Isn't that like, the hallmark of intelligence?