For that matter, isn't the (or one) reason for having a backup so that errant deletes don't obliterate everything?
Fortunately there is no strict time limit on completing this process so a design that looks like "and after X months it will have aged out of our backups" appears to be considered reasonable. You are still responsible for making sure your backups are safely destroyed.
In the long term everything suffers from "data decay". It's just too hard to keep old files around forever.
E.g. there were comments I made on Usenet many years ago. Google has previously attempted to preserve those, but they seem to be fading away into the ether. That's okay by me.