A lot of people think that the Republican Party is heading towards irrelevancy demographically because of its increasing trend to the right unless there's some kind of significant change. I'm less curious as to whether it will happen than I am curious about the mechanics of it. How could a party disappear? How could another rise to take its place? It's hard for me to see a 3rd party growing like that or the Republican party disappearing like the Whigs did. Any ideas on what will happen if these demographic predictions are correct? Will one faction take over the Republic brand while another heads out on its own? WIll both parties change based on new wedge issues?As far as the future of the Republicans...I'm with those who believe that Latinos will become "white" (that is, they'll be thought of as part of the majority "racial" group) and that Republicans will compete for the Latino vote the way they now compete for the Irish or Italian vote. I do think in the near term there's a chance that Republicans could box themselves into a corner that would put them into the minority for an extended period thanks to demographic shifts, but I think it's unlikely in the long run.
On the larger question, my general sense of this stuff is that a two-party system is more or less inevitable given the US electoral system, but that the permanence of the Democratic and Republican parties has something to do with various "reforms" that make it hard for either to be replaced. Ballot access and campaign finance laws have favored the existing two parties. That certainly could change...let's see, for one thing the campaign finance thing is less of an issue now than it was a few years ago.
I think it's just very unlikely. It's almost always going to be easier for an unhappy faction to either jump to the other party or to take over their own party than it is for that faction to build a new party from scratch.