Balance of probabilities may say the landowner is responsible for what appears to be a rotten tree falling over. Some may try to weasel out of responsibility by saying act of god. To my mind you would first have to prove that there is a god! DOH! Its one for the thieves in suits, sorry, I mean lawyers to sort out. I am just glad no-one was hurt and wish them luck to get their pride and joy back.
If it were me, I would have an arboreal expert there straight away to assess the tree/roots/ground to help the claim before the council/landowner get rid of/hide the evidence.