Regarding Revoking User Ids & their effect on charts

Hi All,
I have a doubt regarding users in RTC Project Area.
The users are added into the RTC Project area with a process role. depending on the team, the user will be added to a particular team area.
He works with that team for an assigned duration. Once that iteration or sprint is completed, the user will be no more working on that project.
Now here is the question.
1. How to revoke that user from the project as an administrator. Should we revoke the user, from the project area only?
2. Once i Revoke the user will his efforts be counted and visible in the charts for that iterations he worked on?
As i checked with one of the user after revoking his name from a project area, his name is still in the team area.

Please suggest me, as revoking should not have any effect on the charts and reports