So far, they’ve published the successor Beta on or before every expiration date. The announcement at the top of the forum ([url]Scrivener 3.0 Beta - Release Candidate 10 (Download Links & Change List)]) will be updated with the new link.
If you’re worried about losing your work, open the Beta and ver 1.9.x at the same time, and copy (Select All, Drag and drop) your entire Binder from the Beta to 1.9 in a new project. Save the 1.9.x copy as a backup.
And if, for some reason, you can’t get the new Beta release to work, and you forgot to make a backup into a format 1.9.x can read or import, reset your Windows date to December 14 and don’t allow it to update from the internet until you’ve made a backup.
Personally, I don’t worry about it. As I mentioned, they’ve beaten every deadline with the released Beta versions.