You can inactivate a user or remove them. If users are inactive, they will still be shown in lists, and all of their data will still be searchable.
On your list of users, make sure that you have selected Include inactive to see any users you have marked as inactive.
If you choose to remove a user, you will not be able to search for them or filter by their name. You can remove a user by changing the user's status on their Edit user page.