Angels
With no way to tell which of the three locations hid not only Alastair but God as well, at least until the barriers came down, Castiel remained separate from each of them, eyes closed as he focused on trying to feel how each of them were doing. It was a decision that tore at him. His orders had been to protect the Winchesters and he wanted so much to be with Ruby, to protect her from what was happening.
But what if one of the other two groups were successful?
Ultimately the pain of being denied the Almighty's presence outweighed both his own desires and his orders, so he waited for the barriers to come down so he could know where he needed to be.
Finally he felt something. Finally.
He wasn't even sure which location it was, just the need to be there. He opened his eyes, his face determined.
"There."
He could feel Her again. The relief was intense. Now it was time to get Her back.