If he really gets a good grip on your neck and you feel like your head is going to get pulled down, you can always grab around the waist and pull your opponent in really tight. The main thing in the clinch is keeping the guy very close and never letting your head get pulled down even when someone is putting all their weight on your neck. Muay thai is a sport, so basically, like the guys said above, the ref will break it up. Learn to control the clinch and you won't need to escape. But you need a good coach to really learn to fight in the clinch.