What would happen to a deity such as Ebonarm(let us assume he lost his worshipers in Hammerfell)? What would that entity be? A lesser spirit of even lesser power? Ebonarm seems as if he can walk the surface of Nirn.

Guess some points would help for organization.
-What is something like Ebonarm?
-What would he become if he was no longer worshiped?

If Ebonarm is a daedra, nothing at all. He's forgotten, but can still act like others through its daedric artifacts, its shrines if they are rediscovered, etc. Or maybe he's busy with Jyggalag lol

If he's an aedra, or perhaps an aspect/dichotomy of an already known one, its ability to manifest through blessings, visions or its artefacts should be quite diminished (given than the other gods don't really manifest themselves so often). If no one praise him nor maintain its shrines its artifacts should be the only things that remains of it.

If a god is forgotten, then that god seizes to exist.

Ebonarm seems different though. He seems to have taken an active role in the events on Nirn in person without any special ritual. Just poof on a major battlefield or poof god of luck gets created.
What about Talos? Would they not just degrade to the point they became three mortals again and then the dreamsleeves reclamation of their souls?

The Thalmor wish...

It's not about degradation. A lack of worship or belief in a god would cause the god to stop existing. Part of the goal of the Thalmor is to remove Talos from the pantheon and wipe him from history and worship so that he is forgotten and unmade.

The only instance of a god becoming a mortal is the unique circumstances around the Tribunal and Dagoth Ur. Any other god would just stop existing.

Ebonarm hasn't been forgotten O.o there are still masques built to him all over Hammerfell and there are shrines to him in the local guild of fighters chapter and other mercenary groups, also TES gods aren't what other fantasy gods are, they don't rely on worship to survive. TES gods are just the et'ada who live in aetherius and oblivion, no actual worship is needed they just get mortals to worship them because they either want entertainment or care about the mortals and having the mortals worship them as gods is an easy way for their bidding to get done.

Not exactly. The Aedra do need worship to survive, considering the fact that they are in fact, dead, after the creation of the Mundus. And Aetherius is outside the Mundus, which the Aedra in intrinsically linked and utterly bound to. They are the earthbones. Daedra are a different story, and do love to entertain/keep themselves occupied with their mortal thralls.

I actually find the idea of them (Aedra/Divines anyway) ceasing to exist if the worship stops to be a bit of a cop out. Have we ever actually observed it happen in lore? Or are we simply told thats what will happen?

I'm not sure I buy it. I will buy weakened, and I will buy that you can worship something that didn;t exist prior into existance, but I'm not sure about it just popping away if that last old guy with a little shrine in his basemant dies.

I think I agree with you there. However the Divines as I understand the theory are described as being worshiped into a mold of sorts. Maybe without worship that mold that gives them a form disappears and they lose their form dissipating into whatever they were before. In the case of Talos, allowing three mortal souls(Tiber, Wulfarth, and Zurin) to cycle through the afterlife or dream sleeve. That sound about right? In the case of the 8 Divines they would simply just revert to latent potential gods IMO. Just waiting till they were worshiped again and the right mold of peoples beliefs would give the form again.

Probably way off there. Any chance someone could update me on the theory of how the Aedra operate again or a link to a theory or whatever. Is there an established theory or evidence of how they work? I honestly forget and am on a mobile ATM so cannot really look it up.