Do you have an Adagio consultant? If one of my clients contacted me with such a situation, I would log on, determine how to make things right, and then suggest an approach for fixing everything. It would be unlikely they would have to restore from a backup.
Yearend processing in Invoices does almost nothing and is not a big deal if you forget. Yearend processing in Receivables also doesn't do much more than period end processing, mostly it resets the batch numbers back to 1 and it clears out the YTD statistics. However, with a useful add-on called Toolkit for Adagio, you can recalculate the YTD statistics as if yearend had been done at the right time.
Restoring from a backup is a last resort and should be avoided if at all possible.
Steve