Bitcoin will not disappear but will stand as a foreign cryptocurrency just like we have some fiat being a standard of measure to other countries currencies.
why do you even insist on separating the two from each other?
it is like asking which one would survive longer, cars or combustion engines! bitcoin is based on blockchain technology and it is the one that introduced it to the world. bitcoin is also the one that is improving this technology and as the technology grows bitcoin grows and vice versa. they are not separate, they are one thing.
That is why they will also develop there own coin because it will become a means of utility. Having a blockchain means having your own privacy which is what government wants.