I think the average person who resigns would have trouble being reinstated, but Starfleet celebrities get special treatment.
So, if Starfleet refused to let Worf reinstate, Picard could just be like "Okay Admiral, I understand. I owe you one after you saved me from insect parasites. Oh wait, do I have that backwards?"
Didn't Sito Jaxa try to resign in Lower Decks?