Not long ago (two weeks?) a Syrian airliner was impounded in Turkey for several days because of a suspected cargo of arms.
Even that aircraft was on its way a couple of hours later once relieved of the offending kit...
I suspect naughty owners will forfeit their toys once the authorities are able to demonstrate a link between the operation of transporting illegal items and the ownership of the vessel/vehicle/aircraft.
Where the pilot of a rented aircraft becomes involved in illegal activities without the knowledge or suspicion of the owner, the aircraft could at worst be impounded as part of the evidence chain.
Unless the authorities can overcome the presumption of innocence on behalf of the owner, the aircraft will eventually be released from the evidence chain to the rightful owner.