Depends at what rpm/load the chain snapped. If it snaps at very low rpm/idle, sometimes you can get away with it. Without any load on the cam, the valves will try to snap shut pretty quickly. If the chain snaps at motorway speeds or high load.....your chances of no damage are slim!
Fit a new chain, compression test it and go from there. You'll need a new chain anyway, so won't hurt to quickly do that before removing the head.