It has been decided already. BTC works in every single department. The only way BU can cause the disaster-hardfork is if Bitmain invests even more millions on hashrate to cause teh 51% split, then we will see the hardfork but people will quickly dump BTU for BTC because a coin with inferior software centralized in china is just nonsense.
I do not think the hard fork will happen below 75%. The hard fork will be decisive. They will be no prolonged battle.
It could, but that's just not a smart thing to do for pools in financial meaning. In order to mine blocks more or less risk free, you need a larger part (preferably much higher than 50%) of the hash rate to support the exact same block setting as the one that you mine. Without this support, you are throwing away precious block rewards (which can be seen as capital destruction). Basically, everything that they do could harm their operations, which is also why this is taking so damn long to settle.