Deleting a model permanently deletes the model from OneClick and also the Spectroserver database. It would be completely removed.
Removing a model does not delete the model from the Spectroserver database it only removes it from the location you are working in.
In the example of a Global Collection if you delete a model that model is no longer in the Global Collection, and also deleted from the Spectroserver database permanently.
If you were to remove a model from a Global Collection that model is removed from the Global Collection Only. That model would be present still in the topology or other locations and locater searches and is still present in the Spectroserver database.