No one knows if the hardfork (split) will happen or not. BitcoinUnlimited leaders have talked about needing 75% of the hashrate before they will initiate a fork. It is difficult to imagine them reaching such a threshold in the near to mid term. Alternatively, I could imagine rogue miners attempting to activate the BU fork at something over 51%, but this would be much more chaotic and unlikely to succeed both technically and financially.
You can monitor the BU hashrate as well as segwit and other proposals at: https://coin.dance/blocks
It has been opined in the press that the price of bitcoin could decline about 50% in the leadup to an announced split, which my gut says is probably about right. There is also the issue of bitcoin being throttled so long as no improvements are made. This is why the altcoin market has doubled while bitcoin price has sagged, and many of us have more or less pulled out of BTC for the time being.
Because many of which have the same thoughts about it so bitcoin prices plummeted. But it makes sense if we tend to play in altcoin while waiting for the latest developments of bitcoin.
But deep in my mind, BU concept will actually appear as it will facilitate proposal for a real regulation in future. And of course, this possibility will make bitcoin price is getting down again until an unspecified time. BU will have a separate system from the original bitcoin, so the number of BTC that we have now will not be separated into two parts