If Republicans go the way of the Whigs and we are left with only one party, it would be a disaster for both our people and our democracy. But it won't go that way.
In the future, there will be two reality-based parties that both have their origins in the current Democratic coalition. The future is now in Seattle. Of course, journalists still currently assume that the GOP will always exist and so they see the birth of a new party not as necessary corollary to the Republican demise, but instead as a threat to "centrist" Democrats (the lefty press sees it that way, anyhow): A Spectre Is Haunting The DNC.