They’ll just embarrass themselves and risk a loss depending on the case.
WV Sen. Machins will probably go with the GOP as he is up for re-election, and should be a Republican anyway.
That's exactly how liberal darling William J. Brennan began his career on the SCOTUS.
While Obama can't make a recess appointment of Garland without the GOP Senate declaring a recess, the GOP controlled Senate can/will call an early recess for a Trump recess appointment - that will last till January 2019.