Nobody can shut down the internet,because internet is a network of servers.Can you shut down all of them?
That's why nobody can shut down the blockchain.As long as there are miners,the blockchain will continue to exist.By the way,bitcoin can be printed on paper.Nobody is saying that bitcoin will be 100% digital.

We already have a global currency.It's called US dollar and it's a pretty shitty global currency.

Global currencies are currencies that are used throughout the world and everywhere. so it's impossible for all to be internet-based. because not all countries are able to support the internet network, and not all regions on planet earth have internet networks. so international paper money is still needed, namely dollars in paper form, bitcoin is not able to provide all the needs of people around the world because bitcoin can only be used if there is an internet connection.
i understand your point but from what i observed bitcoin is already supported and being used by majority of the countries , that's why it is already considered as a global currency . also , internet is not new and im sure that almost all countries in the world do already have an internet because internet is also useful for everyday need . also , i dont think that usd alone is a global currency because i think every currency can also be consider a global currency because there are money changer/exchangers on every country where you can convert any currency according to your choice .