Endpoint Protection

I have a few remote deivces that are in my SEPM that I want to remove SEP from, however I do not have any easy remote access to these devices.  I was wondering if I could select the option to  "Enable as Unmanaged Detector" and them delete them from the portal.  Would I get the use of my license back for this one agent?  

Enabling as an unmanaged detector is irrelevant. It would just tell them to report back on clients without SEP installed. You can delete them to free up a license but they'll take a license up once them come back on but you can then remove SEP if you get the opportunity.