Don't some manufacturers even provide utilities to permanently change the MAC of a NIC? It's completely untraceable.
Yup. Which is why 99% of the time when these attacks happen, X company threatens them with legal action (just like Spie stated) and eventually when the DDOS attacks stop (like now) the issue slowly fades away. The culprit loses the company a couple thousand and never caught and everything is forgotten within a few months.