I can see the GOP nominating someone who is cautiously pro-choice. That is, they oppose overturning Roe or making abortion illegal, but they sill support waiting periods, parental consent, ultrasound requirements, etc., and still express a general desire to limit abortions with particularly strong condemnation of sex-selection abortions (female infanticide). I can also see the GOP platform reflecting these views, which would be considered "pro-life" by pro-life Millennials (though not by staunch pro-lifers).
Such a Republican would also put in a good word for pro-life crisis pregnancy centers. The pro-choice (pro-abortion?) activists would probably not be satisfied, but at least a major issue of theirs-- that the GOP would force women to have dangerous, back-alley abortions-- would be neutralized.
As for pro-life Democrats: I believe it is a complete lost cause. Such a Democrat would have to repudiate nearly a half century of evolution in Democratic thought, going back to McGovern. While there are still some pro-life Dems out there, there are not enough to nominate a candidate in my opinion.
A pro-life Democrat would look a lot like a Pro-choice Republican except for maybe Roe. Maybe the Democrat would sign a post-Roe personhood law if it had a reasonable number of justifiable circumstances.