There was a question on r/DragonAge regarding the purpose of the Old God baby, considering that since the original Warden should be dead and no actual baby should exist according to the Bioware writers’ canon. I posted my answer on said reddit, but for tumblr’s sake, here’s what I think will happen for Inquisition if you chose to have child with Morrigan.
Just putting this out there:
It might have been a bug, but in the DA:O epilogue I think it says Morrigan is pregnant regardless of whether or not the Warden lives/chooses to do the ritual. So assuming it’s accurate, I was under the impression that Morrigan finds someone to do the ritual with, and the Old God baby is born in any case?
The thing is that because the Warden died in order to kill and destroy the Archdemon, both their souls were destroyed in the process. Even if Morrigan were pregnant, and she has a child, the Archdemon’s soul would not have transferred because the Warden’s soul combined with and destroyed the Old God’s. There’s nothing left (or at least there shouldn’t be).