If you clip their wing feathers very short they cant fly and are very easy to catch so if you clip their wings you could let them out if you stay with them. I would try it with one bird at a time or one person per bird in case they go in different directions. With clipped wings, you could put them in a pen with small sides and watch them from a distance to keep predators away.
But never let them out alone, like preciouseureka said they wont come back and are easy targets for predators.
With clipped wings they can't fly very well, and they can't maintain flight, but they can fly. I tried it with my very first quail as I was keeping her in an open-topped pen in my bedroom. She regularly flew up to ceiling height when spooked (so around 7ft) - easily enough to escape if she were outside - and she was fast! Not worth the risk IMO to try and free range them.