Tik Tok said they'll fully shut down. They'd rather go dark now than have a slowly-degrading experience, since users won't be able to update the apps.

It makes sense to shut down the app in the US immediately rather than be unable to update it- but does that necessarily mean they would also shut it down outside the US, or access directly via the website?

Why would the experience degrade because US users are disappearing?

There are countries other than America.