"You see, killbots have a preset kill limit. Knowing their weakness, I sent wave after wave of my own men at them until they reached their limit and shut down." - Captain Zap Brannigan
The military operates that way with 99% of their personnel, who are grunts, expected to only ever follow orders, to never think for themselves. They're expendable cannon fodder - think of them as pieces of hardware in a software company. But with the 1% at the very top (basically just generals), I'd say the bus factor comes into play, same as in any other organisation - certain individuals have all the knowledge of certain domains, and if enough of those individuals are taken out, the wheels grind to a halt. That's why targeted assassinations happen to the top brass.
Sure, if you manage to assassinate the entire command chain, things will go pear shaped.
I dare say you could likely assassinate half the command chain, and the military will still managed to get where they need to be, when they need to be there. Military command chains have levels of redundancy that civilian organisations wouldn't dream of.
As a concrete example, it's estimated that the British lost ~40% of their officers in the Battle of Albuera, and they still managed to repel Napolean's forces.