If Apple tells you to take a hike, and then subsequently disables the email redirect -- you're completely SOL. You'd have no way to reach out to the user anymore, unless you took other identifying bits of info. And if you did that anyway, that defeats the purpose of AppleID to begin with.
Most users will probably not even be tracking what autogenerated email they're using, hence you no longer have a way to reliably reconcile what user had which account.
Regarding the GMail specific case though, I fully agree. Being banned by GMail is a company ending thing.