Any power not explicitly granted the Federal government in the Constitution devolves to individual states, so each state would have the power to decide constitutionality as a matter of state law.

If we're going by a strictly textualist interpretation of the Constitution then this is the only valid option, barring a Constitutional Amendment to actually give the power of judicial review to the Supreme Court.

Is it absurd and insane? Yes. But so is determining law by in essence conjuring the ghosts of dead men.