Personally, and this is just my opinion, I don't think it's a good idea to send her to the human world in this state, to be honest, we only a few good person in the world we living not not so different than underworld just that they have magic and we don't, it cruel alright, not like a lot of people will see a person laying around in a dark alley let along call for help, they just continue their work and don't care about the world, let along a woman, unless after the door open she got send into hospital bed like straight in for people to help, or she get back her strength after return but do i mentioned that she just give birth not so long ago? Standing straight already a problem.
Counter-Point: Your opinion came off as incredibly inattentive for a reader of this manga's world-building.
Merize simply cannot stay in the demon world, dead or alive. Had she remained, she would have continued to suffer and likely become a victim of human-hunting/eating demons. In case you haven't paid attention, we know demons can become frenzied in the presence of human blood - with unknown consequences if they consume human meat and bones (let's not forget the crazed demon that is Iruma's destined enemy).
The demon(s) making the decision to send Merize back did not make the decision out of compassion (most demons simply do not know nor understand the idea of compassion). But the decision was made simply out of their own self-interest in preserving the status quo and for the sake of stability. Henri Azazel was a one-of-a-kind demon in which his own bloodline power overcame his innate demon's desire to consume human being (now if Merize not been a woman... well, let's not go there
).
Cynicism and pessimism is fine IMO (I'm quite cynical myself), but the alternative of not sending Merize back to the human world very likely have been chaotic for the demon world. One could cynically say the demons made the decision to dump a dying woman back to her human world to avoid a massive fallout of keeping Merize around in the demon world.
On your last statement, if you paid attention, the demons providing the care already applied their magic and whatnot as much as they can on Merize based on what they knew at the time (she certainly didn't seem to be in pain and all her limbs are intact). So my best guess from the current reading thus far is Merize as a normal human cannot breathe demon world air for long. Kind of like the best athletes and healthiest person ain't gonna live much if they're trying to breath in areas with 200+ Air Pollution Index
.
Thus Henri knew he had no other options and concluded (in tears) that sending Merize back was the only chance she has at surviving.
