User's session persist after permanently deleting his account in glpi-project/glpi. If a user is logged in, and an admin decided to delete his account permanently, the user is still able to perform his normal actions until his session gets expired. If a logged in user with admin role is deleted permanently, he's still able to delete other admins permanently, and if they are not logged in at that moment, they won't be able to access their account in the future.