If it helps any, I've had a Silva baseplate compass for around thirty years. It's been around the world, loose in rucksack compartments, pockets, boxes and crates, and who knows where else. It still points north (unless I've been going the wrong way all this time). It is a bit worn though. I think you'd have to put a fair amount of effort into somehow demagnetising a compass, and I suspect they're more robust than they look.
As an aside, in addition to the watch method, you can use your extended fist as a makeshift sextant. The vertical fist with thumb slightly extended will amount to 10 degrees. Knowing this you can work out the sun's elevation. You can then use your feet as a protractor. Point your feet together at the sun. Then adjust one foot, pivoting at the heel to make a sort of splay of the feet to the equivalent number of degrees. This will then point to where the sun rose on the horizon (assuming it's the morning - if it's the afternoon you work out where the sun will set). You would need to adjust for the fact that the sun only rises east on the equinoxes, and on the longest and shortest days, approximately south east and north east respectively. With practice this is fairly accurate. This all for northern hemisphere though.