Some scattered thoughts,
1. This isn't news, but the Human Life Amendment is not going to happen in the foreseeable future. Any Republican presidential candidate who makes that their abortion policy and makes that policy a centerpiece of their campaign is really hurting their chances of getting elected, and even if they do get elected, the Amendment will not pass Congress. Focusing on the Human Life Amendment as an immediate goal is worse than just bad electoral politics. It is a waste of pro-life energy that, if it were better directed, could lead to better policy outcomes and better position pro-lifers to make future gains. This does not necessarily mean changing the Republican platform, but it would mean the Republican presidential candidate might avow that they won't pursue policies that they are not convinced have majority support.
2. Pro-lifers should not let themselves get taken for granted. There are commitments that pro-lifers can demand without hurting either the Republican Party's or the pro-life movement's prospects. At minimum, pro-lifers should expect that the President would pursue popular abortion restrictions (especially on public subsidies) and commit to judicial appointments that move the abortion issue out of Anthony Kennedy's head and into elected legislatures. They should also expect a Republican nominee that can, when asked, make a principled pro-life argument - even if it is not central to that candidate's message. One might argue that the assertion of pro-life principles by the Republican presidential nominee will repulse some voters. Maybe, but how many voters that were gettable by Republicans will be repulsed by the mere knowledge that the Republican candidate is a pro-lifer? Probably alot fewer than the pro-lifers who will stay home when they see that there are zero pro-lifers among the two major party candidates
3. For coalitional and demographic reasons, Republicans will have to maximize turnout among their base, win over white persuadables who don't self-identify as conservative, and make some marginal gains among Latinos and Asians. The politics of abortion will be secondary, but can be nontrivial in both mobilizing social conservatives and making some gains among nonconservatives. A combination of an incremental, majority-supported policy agenda and a focus on the abortion extremism of the national Democrats and President Obama personally could be a vote winner if Republicans also have a winning economic agenda and message.
4. Republicans have not been losing because of abortion. The one time during the last campaign that abortion came up in a big way (during the Rick Warren thing), the tactical advantage went to McCain. During the financial crisis, not so much.
5. Abortion is the easy part. Crafting an abortion message and policy agenda that can mobilize social conservatives while minimally alienating persuadables who were not committed pro-lifers is something Republicans have been doing for thirty years. I think they could do a little better, but it is the least of their problems. Crafting a positive winning message on market-oriented health care will be much harder and this is an area in which Republicans have very little history of political success.