If indeed American sites decide to wall themselves off from Europe than you are correct. If, however, American sites like Facebook, twitter and Google decide to go along with them we'll get stuck with the same rules by default here. Of course that will hasten the demise of Facebook twitter and Alphabet (which would be a boon for the free exchange of ideas) I also think this heavy handed attack on the open and free Internet by the EU will light the Euroskeptic flame in millions of apathetic, apolitical Europeans overnight and thus hasten the demise of the EU overall.
So this could turn out to be a great thing. But its going to suck in the short term.
But who knows, maybe Italy will bring down the EU before this is implemented
And yes, this does kind of light the fire under me to get off my ass and pick a good VPN (maybe I should start a discussion thread on that).