In my opinion, keeping the project information distributed throughout the team is the responsibility of the project manager or the management in general. Because, in my previous project, we had a contractor working on a key project for quite a long time. We have asked for some additional resources(people) for backup but of no avail. One point in time, he really had to leave the company because of long contract durations. He ended up documenting what he knows well in paper. The person who took over still had to go over a lot of things to really catch-up but the documentation really helped.

On the other front, in another project, we had a strategy where the developer has to prepare a design document describing briefly the following and reviewed by a subject matter expert before he starts development:

1. What is the problem reported?
2. What is the suggested solution approach?
3. What are all the things that need to be modified?

This document really helped any new team member who comes on board.