1) Cougar - very unlikely. Cougar attacks are rare in general, and even more rare for one to attack an adult man.
2) Faked his own death - Again, unlikely, but people have done it. No way for any of us to know.
3) Murdered - unlikely, and probably kind of hard to execute without detection is sounds like? Also, what would be a motive? Seems pretty unlikely.
4) Guy either got heat stroke or hit his head and ended up buried under brush, low spot, or some other area that is pretty much out of sight. If he did indeed die, and it was hot out, his body would likely become identical to surrounding temps pretty quickly I would think.
None of the options are likely, but then that would make sense for someone disappearing in such an area. Very low probability event. Obviously hope he's okay and wish his friends and family the best. Tragic no matter what.