Update: Yep, Jailbreak still works! Phew.
Update (code BAD): We take it back about our backup working properly. Despite the fact that we had a couple of error messages during the upgrade which seemed innocuous, this iPhone update wiped out our device and refused to restore our last back backup, instead creating a new backup based on a fresh restore. In other words: we just lost everything on our friggin device and the automatic backup is gone.