Deadnaming is never okay. This is completely inappropriate and hurtful. Imagine if someone got married and their family kept calling them “Ms. MaidenName” behind their back. That’s obviously inappropriate and they should be angry about it. IMO there’s a very short grace period for deadnaming and then it’s no contact. Nobody ever comes out with a bunch of excuses about “oh it’s so hard, I’ve known you as Ms. MaidenName your whole life”. It’s easy to respect someone’s identity