User blog comment:Twilight Despair 5/Abaddon as the Season 9 Big Bad?/@comment-82.34.210.166-20130419035817/@comment-1509826-20130419210157

Well it states that they get banished from earth and trapped in hell, with the door way's sealed. As there aren't any actual doorways between Hell and earth, except the devil's gates which aren't open anyway. It stands to reason it means it would be made impossible to summon them. As summoning is the only way they can get to earth (except for very powerful demons which can teleport between, presumably they would also loose this power as I doubt God would miss a single trick) as for the purgatory gate, how would that help them? Clearly demons are unaware of it, and for all we know they can't use it in the first place, and if they get into purgatory all there going to do is have to battle the monsters, as you seemingly can't absorb while anywhere other than earth or hell. Even if they do get into purgatory they still can't get to earth as the portal only works for humans.

And as for the souls power, if they get it all they can do is battle amongst each other, all trapped for eternity.