Can BPD even be treated with talk therapy? That's all LLMs would be used for afaik, it's not ever going to have a long term plan for you and check in

Yes, afaik BPD is the only Cluster B diagnosis with documented remission rates, when using a mix of therapies that normally are based around DBT.

Not sure what you refer about "talk therapy" in this case (psychoanalysis, maybe?), as even CBT needs homework and check-ins to be done.