I've seen this happen. Especially after 2002. They'll come back. I'd considered becoming independent, but I am waiting to see if we can revive the party in 2018 instead of just giving up.
Why leave at all? Assuming you're not an older boomer, then it must be said that we've grown up in a conservative age and despite the sea change towards liberal ideas, we still live under a power structure that benefits conservatives (both artificial and natural). Republicans will lose power eventually, but not if everyone abandons ship because things are not happening fast enough. Elections take place over years, after all. It takes time!
It's not like Republicans didn't face a similar situation over a generation ago. They had a presidential winning streak before they were able to sweep the states/Congress, but before that they were in a far deeper hole in Congress than Democrats are now, for 40+ years.
The reason to leave is why a lot of people might register as Republican- to help nominate moderate, libertarian, or mainstream conservatives that can at least reign in the excess reactionary politics. This would probably be considered if the straight R ticket wins 18,20, and 22. Democrats were thinking that as a Plan B in 2006.
