When someone leaves your company the first thing you need to do is take away their ability to log in and do anything. Here is what you want to do as a manager. Log into the server side and change their company email password so they cannot access that account.
Find the persons account in the application and change their password there as well.
DO NOT Change their role. There may be a lot of things that the person has done that you will need for your records. So the only thing to do is block them from the account.
This will protect you from whatever a disgruntled employee will do.
When you set someone up as part of your company team, create them their own email address that you have control over. More often than not when someone leaves a company they can be disgruntled and wreak havoc and cause you a lot of headaches. Company emails are a great way to mitigate this, additional emails are free and unlimited. Furthermore, you should put it in your policy that a team member can only use their company email when it comes to your business. This way you have control over the messages and communication that has went on during their tenure with you.
Company emails are created on the server side and not within the application itself.