The American public would be more informed about the Galileo and Cassini missions, and especially the Mars rovers, because the networks would have kept calling Sagan to do interviews about them. Until Neil deGrasse Tyson came along, there really was no "Mr. Science" to the American public, and the media doesn't turn to Tyson a much as they did to Sagan.
Imagine how amazing it would have been had Sagan produced a follow-up mini-series documntary, thirty years after the original Cosmos. A lot has been discovered since then, to say the least.
I imagine he would also have been a major figure in the public opposition to the Bush administration, especially in regards to climate change policy.