They belong to winter for the moment, I don't think that trying to summon them from the south side of the wall is a good idea. If it worked we'd be opening a hole for them, and if it doesn't we'll be wasting time.
I'm not sure calling the attention of the void to us by poking it with a summoning spell while we're on its side of the wall is viable either.
It sucks, but perfect victory isn't possible most of the time. We'll just need to plan how to do better next time. Maybe some
Spirit Rush Elixir for the pilots and emergency
Astral Hospice items for the civilians?