What you describe would literally require a perfect storm: 1) a Republican President, 2) a Republican Congress that would be able to overcome any potential filibuster especially since this would require a dramatic shift in the balance of the Court, 3) Supreme Court Justices willing actually willing to overturn or at least significantly modify Roe v. Wade (consider even John Roberts has said the decision to be "settled law"), 4)Pro-choice justices being willing to retire considering the circumstances, and 5) actual enforcement of any pro-life legislation (and such legislation would have to be ones that could and would significantly reduce the number of abortions not just invasive mandatory ultra-sound laws).
I daresay it is more realistic and plausible that the number of abortions would be reduced through the various socioeconomic policies of Democratic administrations (ie heavy social spending, increased guarantees to parental leave, expanded access to daycare, wider access to birth control) then hoping for such a Republican perfect storm. Considering it did not happen during the Reagan-Bush Sr. years or the administration of Bush Jr. when the Religious Right was far more robust than it is to-day the chances of it happening in any future Republican administrations are virtually nonexistant.
I agree that such a circumstance is unlikely, but as a staunchly pro-life person, I do consider abortion to be a form of murder. Even if I considered unborn children as 1/2 a life, that would still be approximately 500,000 murders per year. Even at 1/10 of a life, that's 50,000 per year. Simply the calculations alone make the issue extremely important. As such, even a small expected value of say 10% would accrue 50,000 lives saved per year. So while a "perfect storm" is unlikely, it's absolutely essential in order to save countless lives. I see where you are coming from, because I was and remain a staunchly pro-life person (if you see any of comments on threads relating to abortion)-indeed this was what kept me a Republican as long as it did.
Most likely the Republican Party, in such a situation, would prefer to focus on the economic aspects of their agenda as has been the case in previous administrations. If the Republicans were so concerned about abortion, why was not a Right to Life Amendment actively pushed by the Bush administration around 2005-06? We saw instead they preferred to push a nationwide gay marriage ban and Social Security 'reform", since the former was more popular than an abortion ban at the time thus being able to attract both core evangelical voters and more moderate voters with some conservative tendencies. And the field of probable 2016 GOP nominees-Christie, Walker, Paul-suggest a field far less concerned with social issues than Bush was. Were a conservative Justice to retire from the SC, I can see him being replaced with someone equally conservative but if a liberal justice (or Anthony Kennedy) were to retire than only a comparatively centrist justice (such as John Roberts) would be politically possible. As I indicated above, on the federal courts Republican judges have been just as prone to strike down these state laws on abortion-consider Eric Leroy Yeakel who struck down Texas's abortion restrictions for example. Additionally, the fact is while I do not wish to sound like an abortion apologist, the overwhelming majority of abortions (88-92%) happen in the first trimaster and most that happen in latter stages are due to health complications.
OTOH, several European countries such as Germany have lower abortion rates than the United States does overall despite there being far less of a strong pro-life movement. I suspect that in the United States, abortion rates are skewed by many people going to states with greater abortion availability for abortions and also possibly by underreporting of illegal abortions/use of abortion pills.
Many people here in past elections would have had no problem voting for say Henry Clay or Winfield Scott over the more explicitly anti-slavery candidates of the Liberty and Free Soil parties, even those candidates "condoned" slavery in the same sense pro-choice politicians condone abortion to-day.
Several Republican senators (ie Lamar Alexander and Kit Bond) voted for the confirmation of one or both of Justices Kagan and Sotomayor. The margin is even more overwhelming if we look at Justice Ginsburg's confirmation.
