My mom's longtime partner wanted to add her as beneficiary before he died...

[Betty]

thank you Betty. So even tho they can't locate the bene, and he has no living family members, they won't allow my mom to claim it even tho she had medical power of attorney?

No, it seems not -- she was not bene & is not his wife/related to him. Sorry.

She can talk to an attorney but I don't know how much good it will do.