In The Problem of Pain, Mister Lewis remarks that God is determined to "plant the flag of truth" over ALL of His creation, which fits with Scripture telling us that EVERY knee will have to bow and EVERY tongue will have to confess that Jesus is Lord.
So no, I can't imagine that Mister Lewis would think of God as permitting those evil Dwarfs to take refuge forever in their self-deluded state. Not because God is petty and vindictive, but because His nature demands recognition of truth, every one of those Dwarfs-- along with all unrepentant Calormene villains, AND Shift, AND Tash himself --would HAVE TO be forced eventually to admit without evasions that they were wrong.