TikTok's highly unlikely to get banned, and if it was then 10 new replacements would pop up overnight. Facebook isn't anything like TikTok and likely never could be. Instagram might get close but even then its not the same thing.
Also the display ad market is only useful if you've got people to advertise to. The more Facebook continues to turn into 'social networking for boomers' the less and less they'll make.
Like, I left FB five years ago (after staying there for 5 years), and literally HN has been telling me that FB were doomed for all of that time.
I totally agree that TikTok is a very strong competitor, unlike what they've seen before, but writing FB off right now is probably not the wisest long-term decision.
How many in the US, and how many with desirable advertiser demographics. Selling reverse mortgage and pharmaceutical ads to boomer audiences turns you into television, where--at some point--the audience is going to pass on and leave it behind.