But they can still very easily fire at anyone trying to get through without permission. Mines aren't a requirement

They're going after a bigger fish, the petrodollar. That dies and the US economic dominance goes with it. No one cares about US sanctions any more. The only sanctions require naval and military force. Ukraine gets a lot more serious as Russian funding comes back quickly through China and India, most likely with the added benefit of imported military hardware.

Economically, the world would suck but survive. Politically, it puts us on rails to global conflict.

They’re smart mines they can control when they detonate.