In reply to Tall Clare:
> the one in Ilkley quarry a few years ago
If you mean the council's 'stabilisation work', the nearest to a classic I think was Wellington Chimney, a 1-star Diff. Curiously, several people claim in their UKC logbooks to have climbed it, many years after it ceased to exist! It has been resurrected (sort of) as Demolition Derby, an HS 4a that is more pigeon poo than rock.
Isn't there a 'chimney' route at Shining Clough where hal;f the chi8mney is no longer there, and it's now a wall?
And not exactly a 'classic' (except in a local sense), but a large part of Park Nab (NY Moors), including some of the best routes, fell down one night a few years ago.