If you heard about the NCIX story where they basically abandoned their servers filled with users data (over 13 years of data) and someone scooped them up and tried to resell them on the black market, one could think that a similar fate is possible.
source : https://www.privacyfly.com/articles/ncix_breach/
Obviously if Facebook was going under it would probably trigger a huge legal process on how to handle the data but it clearly doesn't happen for smaller businesses...
Interestingly, Facebook owns your data. I believe if they wanted to, they could close the company tomorrow and put a facebook.tar.xz of everything they collected on archive.org or somewhere else.
Your data is their primary asset.
(Except if a European office of Facebook did it, then the nationality doesn't matter.)
And it won't matter because the data will be rolled over to drive ads on Instagram and Snap and other attention-properties.
Facebook is the IBM of social media. It's too big to die, and too big to do anything good.
At least that written and TOS or so.