Now I’m not suggesting all your managers take vacations for months at a time. I do think vacations are a good thing – but that’s a different discussion. However here’s why I ask this question about your managers.
If someone is not replaceable, they are not promotable.
A growing company needs promotable people. One indication of how replaceable they are, is how long they could leave before everything takes that trip in a handbasket people keep talking about. And if they can get away, even when there’s no place to promote them to, they can start doing special projects, training and other things that help your company grow.