14th Amendment gives federal law supremacy over state laws. If Congress passed a judicial-proof Roe v Wade law, states would be powerless to do anything.

But my main point is that Republican's long project to pack the courts with conservative judges is useless if they lose control over Congress and the Presidency in the bargain. And that's just what they have done by supporting Trump. And sure, Republicans could always get back in power and make abortion illegal using the same tactic. But the backlash would be they lose that power at the next House election, and the Presidency at the next Presidential election, and the Senate eventually. Abortion is too popular for any Party to actually ban it.