Contacts that quit - best practice

Hey folks.

"Mr. Green" here - new to this Sugar world  

Ok, regarding Contacts that leave (quit) after some time. There might be a lot of history (emails, opportunities, notes, etc) connected to that Contact that is valuable to continue to keep connected to the Account record. But at the same time, you want to identify this Contact as no longer an employee of that Account.

So what is the best practice to deal with Contacts that quit?