I'll take disc brakes over rims brakes any time. If that guy's disc brakes overheated and failed then if he had rim brakes they would have failed even quicker in the same situation. No brakes would work for him.

Having ridden MTB in mud and sand I can't imagine discs failing from mud buildup or wet conditions. Can you bend a rotor? Yes, although it's extremely rare unless you ride hard core downhill or throw your bike into fire pits. But you should be able to straighten it so you can finish your ride, your rims are still intact. If you bend a rim badly you can't finish your ride. Also, messing up both discs is so unlikely that's almost impossible so you can always finish your ride with one functioning disc brake. You can't finish your ride with one rim. But yeah, I prefer cable brakes, not hydro.

This reminds me of CD versus vinyl records arguments. The proponents of older technology will always find gazillion of reasons to prove its superiority over anything new

Adam