In discussion with a friend tonight, he had brought up how he had read about the Dawnguard expansion and mused about the silliness of Harkon's goal (permanently blotting out the sun). Now, in the real world™, we know what happens in such a scenario; things get really cold, mass extinction event, end of story.

So, I started to contemplate such a thing and explain why the above real world scenario wouldn't occur in the Mundus, but I came up stumps. Given that the sun is really the rip in Oblivion from Magnus fleeing to Aetherius, and the main source of magical energy, does it still serve the same function as the real world™ sun in the capacity of generating sunlight/heat?

Is there an explanation to be had as to why Harkon's plan actually makes sense and wouldn't cause a mass extinction event, or is this just a case of foolish villain that didn't really think things through?

Curiosity has gotten the better of me, this time.

That's an interesting point. I always figured since the sun in TES isn't a giant nuclear ball of fire but rather a hole to Aetherius, Harmon's plan isn't really just to use the bow to create a giant shield over the sun but rather a giant cork that serves the same purpose.

And building on that wouldn't blotting out the sun cut the flow of magic into the world, crippling all magic users?

Well, there is always some light in caves, even if there are no light sources...
So if there is light without sun, maybe there is warmth without sun too.

The sun is just a big star…

Ayleid wells recover their magic during night, from the stars…

So blotting out the sun diminish the flow of magic, not cutting it…

Yes, mage characters would be quite weak.

That would be really bad for magic users like the Volkihar, actually.

It would really weaken the flow of magic.

To all those who say Harkon's goal is "silly"...

He's a madman. Logic doesn't work on crazy people.