You are correct, there is a bug in the Skyline Collector, where clicking the DeRegister button does nothing. Here are the steps to DeRegister the Skyline Collector from your Cloud Services Organization.
1. Open the console of the Skyline Collector virtual machine.
2. Remove the generated json files [ rm /usr/local/skyline/ccf/config/generated/*.json ]
3. Reboot the virtual machine.
At this point, the Collector has been deregistered from the Cloud Services Organization. The admin password will be set to 'default'. Any products added to the Collector will remain unless specifically deleted from the Skyline Collector, using the Skyline Collector UI.
Any further questions concerning this, let us know. Thank you Vikram.