So what was supposed to happen when Dagon "walked the earth" after the liminal barriers fade out? Does everything just reset back to the beginning of the creation and start another kalpa? I thought that was Alduin's job.......

Well, Dagon is supposed to destroy Existence. Towers are being "nullified." The world IS technically screwed by the mere fact it exists.

Destruction of the Towers would destabilize existence, for they harvest Creatia to keep existence going. After all of the others get obliterated, the last, I'd imagine, would be the Ur Stone/Tower, Direnni, which I don't necessarily know how that would happen. We also can't forget the existence of the Wheel within the Wheel, White Gold, and the 8 towers around it; such a mythic structure would have undoubtedly bad effects if the Ayleids did whatever they intended to do with them.

All this said, I'm confident the Dawn would return; destroying the "anchor of all existence" would undoubtedly have bad effects for the Aurbis. Recall that Alduin is essentially Anu and Padhome combined and can kinda be seen as a looming force rather than an entity with a direct impact on Nir, like perhaps a Daedric Lord has.

In the end, this is all my opinion though.

edit: Sorry I screwed a name up.

Wouldn't the removal of the last tower just Zero-Sum everything?

Things weren't Zero-Summed before the creation of Nirn either.

Ehhh, while this is moreso a nitpick rather than a refutation of your claim, I don't think Zero Sum would be a relevant term. As stated, the Towers stabilize Nirn and keeps everything anchored. When the anchor is removed, it would all kinda fall apart and merge together in a way at the same time, in my opinion. The Dawn would return, and Alduin would eat the sh*t out of the world and start the next one.

So maybe Nirn reforms itself into its original/previous form ... but that might be zero-sum for the mortals on it eh?

And who knows what Alduin might make for his/its/her 'next world'? Would it have to be a 'world' as we know them to be?

Too often people focus in on Dagon's sphere of destruction and completely forget about his sphere of revolution - the part of his sphere that was completely fulfilled by the events of Oblivion...

As for the rest, yea, destabilization as magick comes rushing in full-force to allow for fullness of possibility and the governing laws of the world fall to the wayside...

Assuming there is a 'before the creation of Nirn'...

They were, um, called Mythic Dawn for a reason, I thought.

Ahhh, indeed we do...

Noted.

I actually wish to restate my thought, in that it wasn't complete fulfillment of 'revolution' as that would have been a return to the Dawn Era - the idea of 'revolution' was still fulfilled though...

He is? I thought he just stomped on things... Wouldn't any Daedric Prince walking on Nirn have similar consequences... insofar as they could do so because of the Towers (and their Guardians???) failing...

EDIT: and wouldn't destroying Nirn/the Mundus cause trouble for the 16 realms that are in between the spokes of the eight etada (Aedra) that helped (erm... well, tricked by Lorkhan) into making the hub, Nirn? Get rid of the spokes... and the places in between are no longer in between anything...

Without the barriers, the Sigil Towers can anchor the Deadlands with Nirn. In theory, the lack of barriers wouldn't do anything without some sort of action from another realm.

But of course, their very nature insists that there would be action... besides, Aetherius plays just as much a role as Oblivion does with the towers...

Is it contradictory that mer built the towers and mer are said to want to tear them down?

Well, I think the Mer that built the towers, aside from the one already there, were trying to emulate the gods. Present-day Merish ideas disagree with this, and seek other routes to Heaven; tearing them down.