had a similar experience recently and can symathize, had a crank snap at the pedal hole on my old fixie while sprinting HARD, hit the frame (also lugged and butted 531 like yours FWIW) so hard I bent it with my leg and cracked my helmet when I hit the ground. Was really bummed as I bought that frame/bike new 22 years ago and have a LOT of history with it, but eventually realized I was very lucky to not break any bones and to have a helmet on when it happened. As others have said, you could get it fixed, but in my case I used the crash as an excuse to buy a Soma Rush to replace the old frame and am very happy with it....