Q1. Is there any way to ascertain that the Mt.Gox bankrupcy was indeed induced by transaction malleability?
Let's say person X (attacker) withdrew e.g. BTC 666.696969 from Gox (or any other exchange). The same person X needed to claim exactly the same amount (BTC 666.696969) from Gox a week or two weeks later, right?
What could be done is to run a query on blockchain data to identify such transaction pairs, initiated from addresses that once had a fairly high value of ''total received'' (indicating they were exchange address) and sent the same amount (BTC 666.696969) twice within a certain period of time.
If someone identifies such pairs, then we might at least get the idea of the maximum possible malleability threshold that went on the Bitcoin network.
We are not sure and cannot be sure at the moment. The malleability can very well be a real thing or just an excuse. Someone brainy needs to investigate this through blockchain data analysis.