Will the Senate demonstrate a backbone on SCOTUS?
The president has indicated that he will nominate a successor to Judge Scalia. He is likely to place the name of a left-leaning justice for consideration. The president will undoubtedly determine to make this selection politically advantageous for the Democrats in 2016 elections. He would likely find a person with acceptable qualifications to a constituency that he would want to show up at the polls in larger numbers than would otherwise have shown up.
The Senate is under control of the Republicans and a skilled parliamentarian in Majority Leader McConnell. He can control the calendar to remove the risk for a recess appointment during the remaining 2016 year. With some thought, the president can be prevented from such an appointment at the termination of this congressional term, as his term ends on January 20, 2017 also. Republican senators understand the critical nature of this appointment for their electoral futures and the nation's (as even Senator Graham has threatened a rejection).
Normally the process of replacing the High Court Justices takes some time, during which the president vets new names (typically up to three months) and then the Senate holds hearings and votes, which can take up to another three months. Under this situation, then delaying the process puts the choice in the hands of the next president.
Obama has indicated that he intends to submit a nominee within one or two weeks. Therefore, it appears that he has already selected from a list of possible choices. These are very likely to be committed liberal jurists. This would change the balance of the Court for a generation. There is nothing more important for the survival of the "originalist" (Scalia's thesis) construction of the Constitution than rejection of this type of jurist.
If the president sends up a nominee from the left, the Senate should quickly review and reject the person. This will take the issue out of the immediate view of the voters long before the election, making the concern more ephemeral and less concrete. The president will likely select someone who has already passed through the Senate confirmation process, making it harder to reject that person. It will demonstrate that both parties followed their responsibility under the Constitution. It will show that the Republican senators have a backbone that they have rarely demonstrated against Obama. It will generate interest in disaffected voters to enlarge their majority for the next term.
Obama himself filibustered the nomination of Judge Alito. He even argued against Chief Justice Roberts (who cast the critical vote in favor of Obamacare). Future Senate minority leader Schumer argued in the past against allowing President G.W. Bush to appoint a justice 18 months prior to the end of his term. Parliamentary maneuvers can be used by either side to gain an advantage. Prudence requires intelligent use of any procedures to thwart the destruction of our constitutional foundations. There is plenty of hypocrisy on the part of both political parties and individuals in Washington.
Should the president nominate a more moderate justice, then the Senate leadership could delay or quickly reject the choice as it sees fit. The decision should be dependent upon the alteration to the balance of philosophy. Justice Scalia represented the most intellectually conservative position on the Court. He cannot be equally replaced, but one can be found with an inclination toward his views. He once explained in an interview that he would dislike seeing his replacement undo his work. It is dependent upon the Senate to honor his request.