Generally speaking, no. There are plenty of connections between ISPs outside the US that don't go through the US that you'd probably still end up with a connect

Generally speaking, no. There are plenty of connections between ISPs outside the US that don't go through the US that you'd probably still end up with a connected network minus the machines in the US. I would guess there would be latency and throughput problems though. If they were really malicious, US based ISPs could cripple the internet by "hijacking" IP addresses that don't belong to them. The internet backbone mostly operates based on trust, if you're part of the backbone you are free to broadcast false routing rules that forward legitimate traffic to a black hole. Still I don't think this would last very long, it's just a matter of time before other ISPs purge the bad rules and get routing working again.