Retain information from former users (ex employees)

I recently asked my success manager assigned to my account about this so I figured I'd post it here.  I've run into the situation where I want to retain context from the project and task comments of a former project manager.  I learned from experience that if I delete the user account, everywhere they left a comment or took an action, it will just say "deleted user."  This makes it difficult to distinguish one former PM from another.  My current work around is to deactivate the user account and switch it to a collaborator so it isn't eating up a regular user license, rather than deleting the account.  This becomes less than ideal since you can technically still assign tasks/projects to these accounts and @mention them.  There should be some limited account type, like a dead account, that retains the users comments and actions, but doesn't include them in the list of assignable or @mentionable users.  Anyone else have this issue?