>If you lost the manager (who is calculating deadlines, coordinating with other departments, pitching for funding, as well as managing the individual developers) the project could run into problems quickly.

Really? In my experience managers can be replaced rather easily, or at least more easily than it is to a replace a single engineer. It always takes some time for the new software engineer to learn the specifics of the project, and even more time to really grasp the business domain. The new manager has stuff to learn too, of course, but in my opinion it's less than what a new engineer needs to learn.

In addition, if you replace two software engineers, you pretty much lose two man-months of work, but replacing a manager shouldn't cause much problems in the first month.