I have done a lot of muddy riding off road with rim brakes and a good bit with discs as well most of it MTB-ing and not as much touring. I have has issues with worn out pads on tour and replace pads often. Once in the Appalachians I feared I was going to be walking the downhills until I got to a bike shop. I lucked out and ran into some friends I had met earlier in the trip and they had some (2) spare pads. The pads I had looked like they had more wear than they did because there were metal ridges protruding into the compound otherwise I'd have replaced them sooner.
The bigger problem IME is that rims wear out with rim brakes. I have replaced rims in the middle of a tour a couple times because of rim wear. It is much easier to replace a rotor. You could even carry a spare if you wanted to. I have gotten to really like discs in recent years and while most of my bikes still have rim brakes, my preference is now for discs.
With discs you still need to replace pads, but less often IME and you don't wear out the rims.