Well, in that case it was for a project that required a very specific and somewhat rare set of skills (IE, you couldn't just throw a dart and hit a web developer). I was friends with a lot of people there, so I know it took them about 6 months to find a replacement, and even then the person was more expensive and had a long ramp up time to become as productive.
That's the big trick is most software companies aren't doing anything particularly novel or innovative that requires particularly skilled or inventive people. Where I work there's largely pocket of innovation where something new is brought into the company and then several other squads take that same process and apply it a few dozens times in a somewhat rote fashion.
Sure, but theres always ramp up time, domain knowledge, and the risk the new person is not as competent as they may have appeared in the interview, even if the skills are commodity
When most of the team can do the work because it's so generic the ramp up impact is more limited and there's usually some small back burner or simple work a new hire can be put on as a test and onboarding project.
