I backed it up and within 20 minutes it had been disabled.
Interestingly, it put it in a state in which it was unable to ring for incoming calls.
I wish Apple would not report that your iOS version is "up to date" in iTunes if you are running a time-bombed beta build. Even if they don't want to support a direct upgrade path from beta to GM, they could indicate in their software that your software is not up to date.
Not everyone can afford dedicated dev devices--even though that is in their terms of use.