What would happened if a group of magi did the following? First of all inventing a casting a Aegis of the Hearth around their covenant, lets say a level 50 spell. Then cast a ritual Daemons eternal oblivion with a boundary target lets say a level 50 spell with a penetration total of above 50. Would all daemons within the boundary with a might less than 50 simply banish and no other daemon with a might below 50 not be allowed to enter? Could all daemons be affected by such an boundary DEO? If that is possible what will be the consequences? Will all diseases that does not have a divine origin simply vanish as there are no daemons to administer them? If the plan succeeds what would be the infernal response? Any other consequences?
Yes. Or at least, almost: A demon in "deep cover" through his Possession power ignores wards, and could enter the Aegis (Noble's Parma)
At least, the infernal diseases would dissappear, yes. Infernal response? All up to you. And it's also different if you stay in your covenant or go out blasting demons.
IMO, you'd at least have some deep cover demons on your hands
I think this is one of the effects of Boundaries. How on earth could you possibly know of the existence and location of every pest and vermin, in the benign farmer-magus spell "Saving the Harvest" ReAn, with the Boundary being the edge of the field.
If you don't know the demon is there, it won't affect it. If you have a horde of demons running around in front of you, and you DOE 50 them (l:30) then they get splattered...but if the demon is in spirit form, you are wasting your time...(and Vis).
It's not targetting them individually though, there shouldn't be any need at all to sense them, like previous people mentioned. I'd be fairly happy with it affecting everything within a boundary. It's a ritual, it'd take vis and time to cast.. if a demon is still in the area after all the effort, they deserve to be affected.