Tl;dr there is a 100% chance McConnell would have gone nuclear immediately.
It’s important to remember that McConnell could use any nominee to go nuclear on all nominees, including SCOTUS.
Any nom would do- judicial, cabinet, anyone requiring Senate confirmation.
There’s no reason McConnell would have to exclude SCOTUS and he’d have every reason in the world not to.
If you think McConnell reshaping the judiciary is a bad thing, consider how much worse it would be if there were even more vacancies for him to fill than there are now.