I worked at a similar company before. Management don't care about that at all. We had our fundamental stone quit due to getting married and moving abroad. They just found another heavily specialized engineer and made him an obscene offer. Didn't take long for him to be on top of the systems either.
The one thing that I am still in awe is that the new engineer had his PhD in chemistry, and never attended a CS class once, but was nevertheless a world class engineer and hacker. Miss working with him.
>They just found another heavily specialized engineer and made him an obscene offer
That's unfortunately not something that most smaller companies can afford to replicate and still be alive.
If you've got unlimited money sure, everyone's replaceable as the problem boils down to having enough money to poach the next best replacement, but hiring the best of the best with guarantee they can take over the most complex codebases quickly without impacting operations, is an endeavor that can sink small companies if the bus factor hits their core.
The one thing that I am still in awe is that the new engineer had his PhD in chemistry, and never attended a CS class once, but was nevertheless a world class engineer and hacker. Miss working with him.