Unfortunately this is only possible in a platform where they have indefinite access to their account. When they leave the company they have no ability to do this. Many don’t even know about their right to do this too.
To get ahead of this, our data office expects anonymity within 90 days of leaving the company. We currently use the anonymisation functionality as part of that. Unfortunately the casual use of names without @ doesn’t get included with this, so it leaves us with an extra effort and uncertainty when anonymising accounts.