Haven't read the LN so don't know for sure, but the vibe I'm getting is that the baby will be a devil, but the mother & Schtrom (sp?) both die in the end. Shin will take in the baby with Cecily & raise the child as their own, due to the devil baby being sinless/blameless for its existence. Maybe even living in the same forest that Shin grew up in.
The baby's excess magic is explained away as being "the child of Shin Walford" & any devilish presence is either ignored by those that can tell (& are in the know) or they come up with a way to mask the devil presence, like the devils do now.