Force delete just purges from vCloud Director's database/GUI.
The thing you want to look into, is why the Edge objects are not naturally being deleted. When you do a "delete" from stranded, we send an API call to vShield/NSX to delete the Edge. If this fails, we should get a message in our logs and there should be an Event in vShield/NSX.
If you have a support contract, I would attempt the delete several times and then gather logs (all vCD cells + vCNS/NSX). It's a little hard to do this via the forums since the logs can contain data you might not want to share to the general public, and the support team should be able to quickly review them.