I’m not sure but I think you can deactivate FB while keeping the messenger app? Sorry that I can’t offer better info and I’m sorry this is happening
Edit: From the other place
Of course one of the more relevant answers about keeping chat history is deleted… but there’s at least some discussion in there.
I also hate social media and technology
I’m trying to work out how worried to be at some rando using one of my emails for their instagram (I’ve changed the password on seeing that and checked logins). Wondering if I should go delete their account. Seeing as I can’t make them use their own email.