If the GOP keeps losing, when would a viable replacement party emerge?

[Mehmentum]

Well, in a hypothetical scenario (which is unlikely to happen) that the GOP stops being viable, history points in two directions.

1.)  After the Federalists collapsed the Democrat-Republicans splintered, leading to the Democrats and Whigs.

2.) When slavery tore the Whigs apart, the Republicans emerged from coalescing of anti-Slavery Whigs, third parties (mainly the Free Soil Party) and anti-Slavery Democrats.

Scenario 1 would involve some sort of split among the Democrats after the Republicans became mostly irrelevant.  Scenario 2 would involve some sort of split among the Republicans, with one side merging with a third party and winning over a large slice of the Democratic party.

Unlikely, but it would be very interesting.  I would consider myself lucky if I could experience such a political transformation.