Hi Maureen,
You actually won’t be able to “remove” the user for this reason. There are records in your account that link to this user and if a user appears anywhere in your audit trail, you will receive an error when attempting to remove it. Your alternative is to uncheck the user can sign in option so that it no longer requires a license. Additionally, you can make the user inactive so that it does not appear as an option in any of your dropdown lists. All linked records such as activities will be unaffected.
I hope this helps.
Audisho