Leave, also on grounds of integrity.
When I was on Facebook, I never had a single issue -- I mostly used it to cross-post photos of landscapes and architecture and RSVP for events, so I don't think this is a scenario where they think I'm a spammer or troll returning to the site.
If I had $$$$$ I'd short their stock -- you can't make it ambiguous if your users can return and expect anyone to make the effort.
Also I'd be interested in the legal ramifications for EU users if this bug effects them -- I can't delete my Instagram now, because the FB SSO was summarily banned without human review. What happens when someone born in a country with more freedoms than the USA decides to file a GDPR complaint due to their algorithmic misfire?
Anyways OP, unless someone sees this on HN and reaches out as a PR gesture, there's probably not much you can do.
I suggest the "GDPR Nightmare Letter".