It's even worse than you point out. DOGE/Musk/whoever is really in charge didn't learn the NNSA staff was critical because the firings cause some immediate impact. Someone who actually knows what they're talking about likely told them about the problems it would cause and the firing squad actually listened. Had they relied on waiting for side effects to understand the impact, it would be far, far too late when you're talking about something like nuclear weapons.
In other words, not only is the strategy wildly likely to result in you learning things are critical years past the point of no return when talking about functions like nuclear weapons, it was completely pointless in this particular case. They didn't learn anything they couldn't have learned beforehand, but did manage to piss off a ton of people with critical skills who are likely looking for the exit now if they even came back at all.
In other words, not only is the strategy wildly likely to result in you learning things are critical years past the point of no return when talking about functions like nuclear weapons, it was completely pointless in this particular case. They didn't learn anything they couldn't have learned beforehand, but did manage to piss off a ton of people with critical skills who are likely looking for the exit now if they even came back at all.