If a draft is created and assigned with a remote key, this key will not be deleted if the draft is removed.

any further tries to create another object with the same key will return an error.

test case:
1 - install the test command located here: https://gist.github.com/pbras/eba5c300eaa1553e3517
this generates a draft folder under some given parent, removes it and shows a message at the end.
2 - run the the same command twice (example: ezpublish/console test:genFolder myfolder SOMEKEY )

3 - on second run, the error message shows:
SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry 'SOMEKEY' for key 'ezcontentobject_remote_id'