Are their Starfleet deserters? Can't you quit whenever you like? Or do you sign up for a set amount of years and are then legally bound to it?
Ensign Stefan DeSeve from "Face of the Enemy" would be another, he deserted when he defected to the Romulans.
One thing always did puzzle me about Riley Frazier, how'd she get out to the DQ? Are they implying that following Wolf 359 the Cube launched a Sphere that travelled all the way back to Borg space with several assimilated crewmembers from the battle? Seems a very odd thing to do in the middle of an invasion (surely they would need every available drone for taking on something the size of the UFP). And they managed to do it without it being detected.