Someone could be trapping so the cat may have been trapped and taken to animal control or the humane society. I would check there first as most strays/ferals are killed after a short holding period.
Also, some kind of threat. Coyotes, intact males, aggressive cats, other animals or possibly humans that are not friendly to strays/ferals.
The cat could be sick or injured.
The cat could be taken in by someone.
Just a few things off the top of my head. Hope your friends comes back soon. Good luck.
