Here's a strange thing; season 4 was obsessed with exiling some of its main characters. We have Worf; exiled from his people for not supporting Gowron. Quark for breaking his contract with Brunt and Quark losing his business license. Finally we have Odo, judged in the Great Link and cast out a solid and condemned to whatever fate befitteth him.
To be fair on the writers, Garak only showed up halfway in season 5, so maybe Garak did go to prison and because no photon torpedoes were fired he got a six month prison sentence? Sort of like Kassidy smuggling weapons for the Maquis, she too was sentenced to six months in a penal colony.