Yeah tbh I'm thinking as well that I could partially dismantle it by removing the left hand sub frame tube (#7) which may make it easier to get the bolt out and inspect it. If the bolt is bent they're only a few quid so it'll be no big deal. It's an old bike, but I don't think it's a particularly shit one! Like you and PGN1 have both said it does seem unlikely that the frame has bent at such a low speed. It couldn't have taken that much more impact than it would have had I just dropped it from vertical whilst standing still. The bar end and clutch lever did take a hit but the bars themselves aren't bent as far as I can tell and I'd have thought they'd be the first thing to go in a situation like this.