If it’s MIT or otherwise permissively licensed, they absolutely can take it over by forking, putting enough work into it that it’s not worth continuing the original version, and then not releasing it openly, or with complicated entanglements.

If it’s GPL or similar, the process is slower. They will probably immediately start a grand redesign which will, incidentally, not use the GPL library. In the short run, they will start a replacement implementation of the GPL library, incidentally permissively licensed. Both will take time, but usually gets there.

Both of these cases are seen all the time.