It is not yet certain that much of humanity will die or not. In the event that humanity is near the point of extinction, we must repopulate the earth. This will be the only good thing about the post 2012 world. Getting to repopulate. We must do this responsibly though. We must refrain from pregnacies in the first year or so. Until we get "back on our feet" Afterwards we will begin mating.
It is difficult to state a strategy at this point, due to the fact that we don't know exactly how many people we will have. If we have few people we must have multiple mates over the course of our lifetimes, and we must make sure we do not mate incest. If you contribute you will mate, we will not have restrcitions on mating because we will need a diverse genetic population.
We will repopulate earth, to where humans dominate again.