You know, back when I first got into this fandom, I plotted out a original fic that took place after a Narnia-like adventure, where the kids are back and (trying to) adjust, and it would slowly be revealed what had happened to them while they were gone. (So having my cake and eating it too, I suppose. *g*)

But yeah, it's interesting because there are certain kinds of plots or tropes that are reasonably common in fanfic, but are very rare or nonexistent in original fiction because they tend to be reaction-type plots.

*ponder* Maybe I just think of Narnia having a Chosen One(s) plot because that's the way I use the Pevensies + prophecy in the Warsverse, although I can see how it can be viewed otherwise. (I have the disadvantage of not seeing how other people use it because I haven't read any Narnia fic for about four years.)