Yes, your purchased products will still work for as long as the underlying technology (flight simulation platforms, OS, and hardware) support them. The Bookmark products do not come with any built-in license protection, there is no “call home” function or key files to enter. Once you have purchased and downloaded the installation files, they should work in perpetuity.
The online Flight Manuals are hosted separately and will still be available on the same URLs after the website has closed.