Do you think Will would marry Margot if she has the baby? I feel like he's that kind of person.
Do you mean had the chance to have since there's literally no way of this happening now or again (with Margot)?
If we're talking specifically with Margot, then I don't think marriage would come into it. It was all a means to an end for Margot, and I can't see Will pushing the issue knowing this. And it's a more modern timeline so I can't see Will thinking 'you're having my child, I should marry you' (especially in this particular circumstance) unless there were genuine, reciprocated feelings there.
I'm hopeful that we'll eventually see both parties somewhat happy with other women. So I would hope that, had things even gone that differently, the writing would never have gone there.
Marriage or not though, I think he would've done his best to be present in the child's life, if that's a better way to answer this question?