There was a Pew Research poll released a couple of weeks ago that said that 2/3 of millenials consider themselves Democrats. Seeing as the millenials already outnumber the baby boomers, they (the GOP) know they're doomed.

Basically, the transition from today's Republican party to something else is going to be like when the Federalists died, got replaced by the Whigs... who then died, and were replaced by the current Republicans. It's really nothing new.