If a users deletes a workspace, doesn't it mean he/she is merely inviting himself/herself "out" of the workspace ? One reasonable behavior would be to delete the local copy of the user's workspace and remove the user from the workspace members list. There may be an (optional) message sent to others sharing the workspace to let them know that this user has opted out, but beyond that there would be no need to do anything else.
There are many advantages to this solution:
- there is absolutely no space wasted on anyone's disk
- every user at any point of time knows exactly who is sharing the workspace objects
- all copies of the workspace get deleted only when the last user deletes the workspace, so there is a simple way for people who have accidentally deleted their workspaces to get it back by merely inviting themselves back in and synchronizing.