Or, this will be the one where he breaks the time travel law by sending a message back to his younger self to ensure he doesn't make the bad choice, aborting the mirror timeline entirely.
I don't think that can work without removing the choice that spun off the mirror timeline. Which would violate Free Will. For Free Will to mean anything, and to work the way Jim seems to have set it up, the Choice must always exist. Otherwise it wouldn't mean anything if you could force the best possible outcome every time.
And the only way to remove such a choice would be to kill Harry before he made it (and deal with that horrible reality) or compromise his will to such a degree that the choice was made for him. I am not sure what would happen then, but I suspect then only one universe would exist from that particular moment, rather than the several possibilities that might have followed (as far as we know, there are only two but I suspect there might have been more).
It feels like Jim is setting this up as Lucifer's goal: a universe without Free Will. Which...doesn't really make sense. Why would the Archangel that rebelled because he didn't have [enough] Free Will want a universe that followed some predestined path? I hope Jim goes a more interesting route myself. And perhaps I have jumped the shark here, so perhaps I shouldn't be so worried.
Ultimately, Uriel said it best. The distinction between Good and Evil is meaningless unless one has the freedom to choose between them.
I suppose then, for choices to still be free, Harry will just have to ride out the consequences. And so will MirrorHarry, wherever they lead.
