McConnell probably doesn't care about keeping his Senate seat at this point. Unless the Democrats can win a ton of Senate seats in 2020 and 2022 to give them 67, while also winning the Presidency in 2020 and holding the House in both years, and then be willing to impeach judges over nothing other than political differences, he'll have accomplished what he set out to do: complete the task laid out for the Republicans a half-century ago by Lewis Powell and put control of the federal courts firmly in conservative hands for decades.
Of course, this could also lead to a decision greeted comparably to Dred Scott being made and Democrats getting elected in droves on the promise of ignoring whatever said decision might be.