Simple Answer : NO.
Because then you loose all links to any object to this user: test/requirements/specifications he/she has authored, session he/she has executed...
Before you do you are being warned about this.
The best practice is to mark the user as "inactive ". This keeps him/her into the database, with all its links.
This inactive user is not counted into your license user limit. So you can replace him/her with a new user at no cost.