Do you take your username from the Sacco and Vanzetti case?
Because you're new here, you can't be expected to know how deeply the "cosmic balance" notion has already been examined. I won't go into that now; but I will go into the difference between Narnia and "allegory."
Allegory means the use of a literary analogy that comments on reality by means of a SUBSTITUTION which effectively ELIMINATES reality for the duration of the story. Thus, when John Bunyan wrote "Pilgrim's Progress," he was temporarily imagining that the City of Destruction, the Slough of Despond, and other made-up locations existed INSTEAD OF England, France, Denmark, etc.
This is NOT what C.S. Lewis did in writing the Narnian books. ALLEGORY is not what C.S. Lewis did.
If I wrote a story which temporarily erased actual reality--not just had a new setting, but pretended that OUR setting wasn't even there at all--and if in this alternate reality I depicted someone who had no roots in real history but who was kinda-sorta like Jesus, THAT would be a "Christian allegory." But that is not what Mr. Lewis did. Aslan is not merely somebody kinda-sorta like Jesus. If you read his WHOLE body of writing, you'll find that Mr. Lewis made it exhaustively clear, beyond any possibility of dispute, that Aslan IS JESUS. Not kinda-sorta like, He IS THE VERY SAME JESUS CHRIST Who walked in our world.
The Narnian world does not kick our world out of the frame of existence, as a truly ALLEGORICAL fantasy would do. The Narnian world is not existing "instead of" our world the way Bunyan did things, but co-existing in parallel space. If you read "Voyage of the Dawn Treader," you'll see that Aslan tells the children that He ALSO exists in OUR world.
When you grasp the meaning of the Narnian stories, you will see that you can no more separate them from their Christian meaning than you could maintain a salad bar that never had any salad in it.
That said, you are free to write what you choose. Only, what LEWIS chose to write was more than an allegory; it was imagining, "What if Jesus did these other things IN ADDITION TO what our world's history records?" People confuse this with allegory because, as J.R.R. Tolkien would put it, the stories have APPLICABILITY to real-world life; but that is not the same thing as true allegory.
Of course, there are lower-scale allegories that can be set entirely inside our own world--like if you wrote about a computer programmer and made him kinda-sorta like Merlin in the Arthur legend--but that wasn't what Mr. Lewis was doing either.
If you ever care to understand what Mr. Lewis actually WAS doing, I urge you to set aside his fiction altogether, and read his autobiography, "Surprised By Joy." Then read "The Abolition Of Man." Only after you've read these would I recommend you read "Mere Christianity," followed by "The Four Loves" and "The Problem Of Pain." When you've read all those, you not only will understand Mr. Lewis much better, but I suspect you will find characters like Nikabrik less appealing. Meanwhile, though, as I say, you may invent whatever plot you like.