No, it isn't. Conservatives will still be a minority bloc if Roberts votes with the rest. You'd still need one more appointment to decisively shift the Court rightwards. If I were the libs, I'd keep my powder dry til the next vacancy. That's the one that will be pivotal - for the future of the Supreme Court - and the country.
("Denny Crane: Gun Control? For Communists. She's a liberal. Can't hunt.")