I agree that even a GOP controlled Senate is not going to say no to Obama's Supreme Court nominees automatically. The President, with the support of the MSM, has a lot of power here. But they will, I believe, say no to the sort of radical nominees that Obama is certainly capable of nominating.
And voting no to a nominee when you know that you have a majority and the ability to stop a confirmation is a lot different than voting no when the outcome is inevitable due to majority Dem support.
In addition, if a retirement or a death of a Supreme Court Justice comes late in 2016 then stalling until after the election would be a real possibility.
Orin Hatch was helpful to Bill Clinton that way (making sure the president didn’t nominate a too-far to the left person for SCOTUS). It was Hatch who came up with Ruth Bader Ginsberg’s name.