Thank you! I fiddled with the ending when I posted the fic on ff.net -- you might want to read that version and compare. Neither is quite what I was trying to say, but I think the second version is slightly closer.

It's odd to me that Charn is so ignored in Narnia fandom, because IIRC, Aslan specifically points it out as a warning for Earth and tells Digory and Polly not to forget it!