If Bitcoin will be banned by all government, then I think bitcoin will die and so the other altcoins. But I dont really see a reason why this would happen, if the government really wanted its people to improve financially, then why ban bitcoin when there is sure income for the people from it.
If there is a worldwide ban it would be possible to happen but I don't thin the government will do that when bitcoin now is beginning to answer the problems of the centralized system. Big companies are seeing bitcoin as an asset where it can help them with their operation and there is no reason for banning bitcoin just being of some irresponsible users who use bitcoin for illegal activities like money laundering.
Yes I agree with you the question is why would world banned bitcoin there must be a reason and I think there is no reason because bitcoin is playing a big role in economy and it make a people facilities and provide a lot of good services for earning so in short word bitcoin is going to help humanity and the people around the world hey love bitcoin.