Hi,
Sorry to hear of your problem.
In your position I would first try installing your backup that you created before upgrading the camera. That will not do any harm. The best act file location is unimportant as you are replacing all that were backed up.
The presence of a valid calibration file set may well remove the 'pending' status. You will need to upgrade the camera again but that is relatively simple as you know.
If the pending status remains, you could try going through the calibration routine but without a Black body or object at the expected temperature, I am uncertain what the calibration routine will make of the situation. It may even abort or offer you the option to abort.
Remember, your original file backup is only valid if you are on the same firmware as when you did the backup. That is to say, if you did a back-up and then updated the firmware, then some files will be different now so the installation of the backup would be a bad idea. The original backup is your best insurance policy though
If you use that, you can do no harm. If you start changing the current file set, you can make matters worse as many system critical files are checksummed.
Good luck
Fraser