I think it might disappear but if internet disappears and if that happens then people will definitely go mad as everyone is dependent on it but I don't think that internet will disappear in future in fact it will be more stronger in coming years, Also bitcoin being replaced as the digital currency is unlikely as well.
That makes no sense, i don't think that is the case, bitcoin can disappear without internet being disappeared from the world as bitcoin is just a digital currency which obviously is too strong but still as said nothing is impossible so that can also happen if suddenly something really bad happens to it which doesn't seem to be happening that soon.
assuming internet and power all over the world remains online and working, then bitcoin is basically impossible to get rid of. even if there are just 2 or 3 miners and equal amount of nodes, it will already be enough to keep bitcoin running. it is by far not as safe as the entire network is right now, but at least bitcoin can continue to exist.