In reply to Graeme Hammond:
Don't think so. I have not heard of any access problems.There are dozens of other routes in Tyla Quarry which are untouched. It looks as if the thief just systematically stripped the first section as they walked in. The fact they screwed the nuts back on after taking the hangers would suggest they are climbers, who know that the hangers could be replaced. There was no attempt to damage the bolts themselves.
For those with the new Gilwern Area guidebook, the routes affected are on the Entrance Wall of Tyla Quarry, page 66, routes 19 to 23. Obviously other areas could be affected but we didn't spot any other missing hangers yesterday.