I don't think a complicated failure analysis is necessary to determine if MOSFET/FET switching technology is a safe "off" mechanism for altimeters. Here is a resource that helps engineers understand basic MOSFET failure modes and perform basic reliability estimates
an-976.pdf "Understanding and Using Power MOFSFET reliability data". Aside from manufacturing defects which would cause a failure in a very short time, MOSFET failures are largely driven by switching on/off cycles, overheating, and over voltage. A properly designed circuit and appropriately chosen component can mitigate these along with burn-in testing.
The article uses has an example with a target failure rate of 11.4 in 10^9 hours of operation. Come on, a rocket altimeter may at most be switched on/off a few thousand times and operated for a 1000 hours. We are talking about extremely low failure rates for these devices in properly designed circuits.
Outside of the cockpit, do we see mechanical switches in spacecraft, avionics, and automobiles in 2021? I suspect the answer is no. Granted these safety critical applications perform FEMA and use rigorous process for mechanical, electrical and software design. I am not advocating that we do that for the hobby. But they don't have a loophole on special circuits either. Yes, they may use hardened semiconductors. But I think the answer we are trying to drive toward is "how much is enough" and can a vendor demonstrate they meet the "enough" for solid state switches.
So take a look at the article, vendors and BOD. I think a few calculations from this article would go a long way in giving us confidence in an answer. Maybe vendors can get an qualified engineer to review their circuit designs (and respecting NDA and proprietary information). Code review. Probably not ... system behavior can be witnessed by demonstration. Again, we are not safety experts, nor do we particularly need to be, aside from a few basics. But we do have a lot of very talented engineers in this forum. Let's put our heads and collective wisdom together and work toward an answer.