They can prosecute the operators of those sites, not like it didn't happen in the internet before. Usually some things survive, but at the cost of extra hurdles (e.g. only accessible via tor, but even there, some people got busted through bad opsec).
You mean the operators of web front-ends which provide access to the exchange? I suppose that's possible. But I don't know how long that will even be the main way that people access them.
