If you have an active subscription, you need to keep the plugin installed and active in order for any new posts you create or edit to be fixed automatically.
Another reason to keep the plugin active is if you are using the options to prevent WordPress from putting Noreferrer on your external links or to remove Amazon links from your RSS feed. Turning the plugin off will also turn these features off.
Otherwise, you are free to delete or deactivate the plugin after your services have been applied. The changes made to your site will remain.