I thought the Daedra wanted to destroy the Mundus so that they could svck up all the raw creatia for their own whims? Or, at least Dagon wants to, but that's 'cause he likes destroying things.
I was under the impression that they just want to play around with it in ways that fit their sphere, for Dagon, this is deatruction, so he destroys things.
But it certainly doesn't make much sense that any conscious attempt to destroy the world is being made, at least, not by someone from that same world, after all, if you really get down to it, while trying to destroy the world makes a very serious threat for your heroes to face, as an evil plan, it isn't exactly very beneficial for you in most cases, especially if it's your own world you're trying to destroy, since generally, one would expect you to die with the world, and the general consensus is that this is not very desirable, so if you're a prospective evil mastermind trying to choose a plan, destroying the world would probably be low on the list.
I could see Mehrunes Dagon trying it due to his nature, but for anyone else, it just doesn't make sense, and even he would be wise to leave something behind so he can have something to destroy in the future, though I don't think Mehrunes Dagon is that wise.
And in an attempt to actually answer the original question, Mundus is screwed. It's happened an infinite amount of times and it's gonna keep happening.
So in essence, the world is always doomed, and keeps going through a cycle of being doomed?
Yes, that sounds consistent.