I like the idea of disk brakes, but I've seen people have far more trouble with them than rim brakes.
Disc brakes do seem to attract more fear and superstition than rim brakes - I suspect this is mainly because people who come to them from a road riding background find them unfamiliar, while they've grown up with rim brakes.
If disc are properly set up there's not very much that can go wrong with them:
- if you have hydraulic brakes and you pack the bike in a way that stresses the joints then you could end up leaking brake fluid - but this is fairly easy to avoid;
- you could dent or bend the disc - but again this is pretty unlikely unless you had an accident that involved falling sideways onto a rock;
- the pistons (or cams if you have cable brakes) could seize up but again this is pretty unlikely.
I think the chances of having problems with discs are no greater than damaging a wheel and not being able to use rim brakes because the rim is out of true.
The key words are 'if they are properly set up' - as with everything else it's worth making sure everything has bedded down before you set off on an big tour.