I think most engineers overestimate their irreplaceability. If a company actually wants you to stay, they'll fight for you. They just choose not to for >90% of engineers leaving.
Chances are, the new hire replacements will be in the same 90%, so it is a wash (minus ramp-up time), but maybe the company gets lucky and finds someone in the other 10%.
I get them being replaceable, but there must be companies would be getting to the point where there aren't replacements, or at least not good ones as the demand for engineers grows.
Chances are, the new hire replacements will be in the same 90%, so it is a wash (minus ramp-up time), but maybe the company gets lucky and finds someone in the other 10%.