Chains can surely snap smashing engine cases. Sometimes the chain can fall on the street with no harm done. Usually when a chain snaps, it's because of an ooooold worn out and stretched chain. I'd look at the bike closely for lack of maintanance. Or lack of really. These bikes are super tough too. Mines been under 3 feet of salt water. It's fine other than a new harness and fresh fluids. Many others here can attest to the love and build quality in these things. Poor maintanance will kill anything. Don't let this new engine be a deterrent either. As long as it runs well and doesn't smoke. Lol. Long wheelies kill TL motors too. Could have been that too if he doesn't know for sure. What's on the odometer?