Bitcoin ain't perfect, and you could say that requiring internet connection is one of the downsides.
And yes, theoretically, having the internet shut down woldwide(for whatever reason) could be a problem. Fortunately though, chances of such problem occurring becomes less and less by the daily because of advancing technology. Starlink seems promising, and Blockstream satellite already exists. And if Bitcoin adoption just continues to go up from here, expect new technologies to be created to decrease the chances of downtime in the future.
Blockstream is actually quite slow for most purposes, especially if you're downloading the entire blockchain through it and I believe it functions on a one-way connection as well. Starlink isn't really a solution, it is still considered the "internet" after all.
All we need is a reliable medium for transferring data across various nodes. It isn't impossible to do but Starlink achieves this through their LEO positioning of the satellite so I'd say thats something to explore. For most parts, signal jammer will still disrupt these, don't actually think there is any better medium to transmit data out there.