There is one other more likely possibility....The Republicans run a pro-choice candidate (rino) and the Christians stay home. 90% of the possible names floating about for our next run are pro-choice Republicans, so it looks like we are more likely to shoot ourselves than have a 3rd party split us like before.
The only way the Republicans run a pro-Choice candidate is if primary voters pick a pro-Choice candidate. The responsibility is squarely on the shoulders of Republicans/Conservatives/Christians to turn out to vote for someone they can tolerate. If they don't turn out, it won't be the fault of the Rep party if someone unacceptable to them in the general is chosen.