Livre d'Or

I think my reading of this part was that only Aslan's trip through death and back via the Deeper Magic had given him the power to save everyone at the castle

I definitely read that sequence in the light of the hymn 'Ye Choirs of New Jerusalem':

How Judah's Lion burst his chains
And crushed the serpent's head
And brought with him, from death's domains
The long-imprisoned dead.

Which in turn is a reference to the Harrowing of Hell, and the castle with the statues very definitely seemed to me to be a sort of Hell, although I don't think I viewed the petrified creatures as literally dead.