You do not have to redo the rating, you need to get in touch with the training organisations and the HOT will decide on the retraining requirements. There is however an issue if yOur IR has expired by more than 7 years.
You could get some ratings back and try to get in from the bottom again if you wanted to fly or there are ground instructor type jobs around. You could consider an SFI certificate, you don't need a licence but would require an LPC on type.
Depends how much you want to fly?