I suppose it could happen. I've never had a contact fail on a bilge pump or at least I've never seen one that was oblivious. In my other life when I was working I had plenty of contacts fail over the years so I can certainly see your point. Mine were always leaking seals around wires or connections failing or the float switch flipping up and getting stuck. Then, my favorite, the float just fell off of the base of a Rule Switch once. I think that was when I decided on an air switch. Mine has a pretty robust set of contacts that could carry a much bigger load then my pumps so that could be part of the reason why they have lasted so long. At work during some of our equipment testing we caused collapsing fields to spike so hard we would get spikes jumping 1/8 wide contacts. Prior to doing some tests we would put "varistors" across the push button contacts of the test equipment to keep from blacking out half a city. It was always embarrassing and hard to explain away when a test went south because you spiked a relay.