Dear respected Christina Berdine Dixon,
Good day! Thank you for posting to Microsoft Community. We are happy to help you.
As per your description, when an employee leaves the organization, the Planner created by hm/her will delete once the account is deactivated. The plans are tied to your organizational account, so once you are no longer part of that organization, your plans may disappear or become inaccessible to you and potentially to the members.
Please understand that our initial reply may not always immediately resolve the issue. However, with your help and more detailed information, we can work together to find a solution.
I'm sorry and I apologize for that.
Appreciate your patience and understanding and thank you for your time and cooperation.
Sincerely,
Waqas Muhammad