You may be stuck and might have to revert to a soft-brick state and upgrade again. I would first try to boot to the Recovery screen and do a Wipe Cache, see if that fixes it. If not, then in Recovery, do a full system Restore. If that doesn't work, and after you've exhausted all other options and attempts to recover control, there's always this thread (
FIX: Soft Bricked after reverting from Jelly Bean update) from CamoMike to fall back on. Note, this thread is certainly risky in that you are essentially soft-bricking the phone on purpose in the process (if it's not already), but then using the method described are able to "un-brick" it and get back on the upgrade path. If you read through the thread, I actually did this with my phone and was 100% successful, so I can attest that it works. Note, I was on the Christmas Eve (Festivus for the rest of us), leak, version 98.72.8, so I haven't tested this method going from the newest OTA version 98.72.16, though my gut says it will work as well.