It should be possible to mark a user as "inactive" so that the user cannot log in, but the user's content is still available through Roller.
This might be as easy as removing the user's "editor" entry from the rolleruser table.
- Remove the inactive/retired blog from the recent posts, hot blogs, planets, and technorati 100
- Preserve the ability to reactivate an inactive/retired weblog
- Disable comments
- Mark the weblog as "[Organization name] Alumni" for bloggers who have left the organization. - configurable by the site admin