A thought: Alduin/Auri-El/Akatosh has http://media1.gameinformer.com/images/site/pages/esv/index.html?es=5, but was stopped by a plucky young hero, as these things often have a way of playing out. However, this didn't stop Alduin from coming back, and trying it all over again in TES:V.
So... what if the player in Skyrim were to... y'know... not stop him? What if beginning a new Kalpa is actually something that needs to happen? Akatosh, a nutbar though he may be, must have a reason for all this.
So... what if the player were to actively help him achieve his goal?
That is the issues with poor tought plots like Oblivion. What if, as a player we dont care or actually WANT to see the circus catch fire.
Well, usually the lazy designers, that stupidly built a sense of urgency without feeding this urgency with real actual facts, towns being razed or see kind of ideas below.
In Oblivion absolutely nothing happens, the portal opens until all the gates places are filled and well, invader get lazy. Pathetic. And you couldn t side the invaders to destroy those ridiculous radial engine driven citizens. Arght!
In SKYRIM, it seems we have the same unimaginative developpers, Oblivion gates have become Dragons (Dragons from a pletora of pther games for the last 2 years)and well, maybe theres a screen or a movie showing that the world ended and how it ended, but by past experience probably nothing will happen, lazy developpers.
Most probably you ll get more dragons, they ll go here and there, if much, burn that and these places and... lives goes on, if we give them credit for what they did in Oblivion and if we assume they haven t learned anything with player criticisism.
They just plainly hope you ll get bored and aventually try to complete the main quest out of boredoom. (My personal case in oblivion, then i shelved the game)
Even because, if the world ends (YEAH!) for some, or the world if saved (YEAH!) for others, how would they handle it in TES VI ? Don t worry if TES V sells well TES VI will exist.
It would be awesome, but i doubt developer will make it, if they even tought about it:
There are many "dragonborns" along myth and SEPTIMS were only A lineage, notorious one but not unique (unless dragons borns only do six after marrying (not likely)and are ever faithfull to their spouses, which we know it ain t true, see Obli.ion).
So, if after a point is reached, or some timer dings, or very inovatively, some random conditions set aleatory at game creation (amongs a list if of pre scripted milestones in game events) are reached, someone else (obviously Dragonborn as well) saves the day and you discover your only one among others. Your life continue but you haven t saved the day and another one is getting feasts, honor, medals, money, wemens or mens or both.
IF you sided "evil" and explictly showed it during your glorious new allies attack, you start to be hunted on sight, like a rat in a couch. That also would be awesome.
IF you sided evil but where secretely participating only giving info and doing shadowy tasks (assuming noone discovered you or was let alive to spread the word) you receive a premium (for good or bad) from the "superior instance", or not, and you can start a new life waiting for modders to bring cool adventures.
Or, even more impressive, if you reached rank enought in the "evil" faction, you are given clues to raise hell all over again !!!! If it fails and you raise hell a third time (each time a diferent and more difficult way) you become the god avatar (where you loose, or not, if you did the right thing, the control of the character)
Obviously latter part of the evil side can be done in expansions or by modders and:
Obviously with this evil option, TES VI begin with a prologue explaining that the evil in TES V was eventually beaten by some hero and the end maybe only delayed.