I was the only full time sysadmin of a 20 person company. I went on vacation for three whole weeks. I was half way around the globe and not reachable. The company still existed after I came back. They did have a problem. They tried to reach me. They couldn't. They figured it out by themselves.

I think we believe ourselves to be more irreplaceable than we are. And if you really think you are irreplaceable then the problem is not going on vacation but being irreplaceable. Because then if something were to happen to you they are screwed.