Think about it for a moment. Would people who now hold XRP for instance buy Bitcoin if Ripple decided to file for bankruptcy? Would Bitcoiners suddenly buy ETH, BCH or XRP if Bitcoin became banned all over the world? I very much doubt that.
You can't ban Bitcoin without banning everything else. But if Bitcoin is ever going to be banned alone, I would for sure switch up to another decentralized crypto - there are very very few projects that would be able to replace BTC in such a scenario from all those many thousands. I'm supporting decentralization as a whole.
Bitcoin is dominant already and i think it is impossible to be ban in the whole world. But if ever it will be banned there is another currency will rise and replace bitcoin (But it impossible). Also it's difficult to predict the future of cryptocurrency ,so let's just wait what will happen next.