The easy answer is that in the American political system, major parties don't die. The last time a major party died was in the lead up to the Civil War, when the Whig Party broke apart on the issue of slavery.

Since the end of the Civil War (150 years ago), we've had the Democrats and the Republicans. While some major challenges have been brought up against both parties, and both parties have adjusted themselves, both parties have also survived.

For more information, you can check out my comment on a similar question: https://www.reddit.com/r/AskHistorians/comments/4tlkuy/historically_speaking_what_do_the_death_throes_of/