how much knowledge is embedded in the memory and experience of the one guy whose pager is always going off and who's getting tired of working 80 hour weeks. How many fixes were done by the one guy who's on vacation and unreachable until October?

Lots. Though I don't have a pager, but a cell phone and it's not going off. And I don't have any vacation scheduled until November.

The question is where and how to keep that information. And how to keep it up-to-date. And not spend 90% of time doing that. So, yes, if I were ran over by a bus (or did decide to leave) my one and only coleague in our team would have a tough time. I'm sure though that even in the first case he'd make it.