Jamming a frequency would cause more of a problem, because now you have an /uncontrolled/ four foot across aircraft flying in restricted airspace. With a controlled craft, you could at least get on bullhorns and try to yell at the idiot flying the drone to stop.

The more advanced models -- the ones more likely to be flown by someone in that situation -- have an automatic return-to-home function that kicks in if it loses the connection to the radio.

On the cheaper models, I'd expect it to simply crash within a minute or two. But it would be interesting to test that.