Nick, I think it was pointed out before on this board that signing a non binding term sheet is not a material event. Probably applies also to termination. See this link:
https://media2.mofo.com/documents/faq-form-8-k.pdf

That said, I personally think that the legal/financial DD and probable (in my mind, people are free to disagree) subsequent drafting of a partnership agreement started by BP in August is still ongoing.