In the cases that Roger (bitcoin.com ) and Jihan ( ant, via, and top ) are not state or corporate interest backed this attack is costing them lots of money/losses. Its unsustainable for the long term. We all know that their intentions have nothing to do #Bitcoin interests for decentralization due to #BU creating centralization through making only large players be able to mine and have proper bandwidth requirements. Note: If you think #bitcoin is centralized in terms of mining now, this is nothing compared to what it can be when you add large blocks.
In the case that they are state sponsored backed, then the worst case is they do try and fork. The network will split between core and BU. In this event some exchanges will list both, most companies that build btc software or provide btc related services will still only work on #Bitcoin. Most nodes will stay with Bitcoin as well. The hashrate might drop in half temporarily but will stabilize around 75% as large centralized players will mine #BU and less competition + lower hashrate makes old miner hardware becomes profitable or worth the risk to mine. #Segwit will soon instant apply on Bitcoin around this time. After this BU will try and use half of there hash to cause problems but it wont work as they have to have some hardware left over to keep BU hashrate on. Most #Bitcoin supporters will sell all the BU coins to and perform different attacks, financially, mining power, node attacks on BU. BU will survive past this as does any altcoin but the threat attackers will be bankrupted or if state sponsored realize that they are getting diminishing returns. #bitcoin price with segwit and payment channels will start to really have a large effect during this time and innovation will start exponentially due to the increase ability to do smart contracts and payment channels, and side chains due to the upgrade.
So the point is Bitcoin will survive in the worst case, not because of the community intent, which helps, but because of natural selection and market forces.