Can anyone seriously maintain that if a Justice (any Justice) were to pass over the next two years, the GOP wouldn't just force Obama to leave the seat vacant until the next Administration?
I think the GOP knows that to raise a stink over an equally liberal replacement for a very liberal justice would just make them look like petulant children, and they probably learned their lesson after the shutdown.
There's likely going to be the votes from the moderate wing of the party to allow a reasonable choice through.