Well, I'd expect that if they allowed 5v through but with a low current limit (I think the default 5v standard states quite a low current allowance). They could catch anything drawing too much and shut the port off until it detects disconnection/other reset.
I mean, if they're thinking about protecting a downstream device, adding this logic would make more sense than just not supplying any power unless a negotiation is made.
In any case, since standard USB ports on a computer will output 5v without anything being negotiated, then it's really no less safe than any other USB port in that regard.
All hypothetical of course. Not convinced things will go that far without some more clear indicators.
The root servers are already spread over the globe. Enough of them are operated by non US orgs too to handle things initially, I suspect that the localised anycast servers located outside the US for those USA based operators would probably go on serving.
It'd be trivial to replace them anyway, and frankly we traffic would be much lower anyway since a lot of the Internet is run by us based organisations.
For domain registration on tlds not run by the us, they should continue to operate fine.