IMO, people often become "indispensable" in software when their responsibilities have grown over time to the point where they're actually doing something that s

IMO, people often become "indispensable" in software when their responsibilities have grown over time to the point where they're actually doing something that should be two (or more) roles. But they've been doing it so long and are comfortable enough in the role that no one realizes it until they have to hire a replacement.