Like most people, I'm not fond of the End Times, and the unworthy successor to Warhammer, Age of Sigmar, or Age of Shitmar as I call it. That being said, there are those among the fandom who want the End Times to be brought into Total War. But if this does happen, it needs a lot more work put into it, and it needs LOTS of changes
If an End Times campaign does decide to show up, it should start (I know this is copying Mortal Kombat 9 but I can't see any other options) like this. The campaign starts in the AOS realm of Azyr, but the bodies of every faction are on the ground dead, even the ascended gods, except for Sigmar and Archaon who are fighting, but Archaon defeats Sigmar. As Sigmar lies defeated, but still alive, Archaon mocks Sigmar on his belief that 8 mortal realms stood a chance at defeating Chaos. He also mocks Sigmar on his belief that he could defeat Archaon, when Archaon had already defeated him in the past. Finally, Archaon tells Sigmar, that when Azyr is gone, there WON'T be another world born from the ashes, the Realm of Chaos will be the ONLY realm of existence. Sigmar, then uses the last of his energy and power to send a warning back in time to Karl Franz to give him an early warning of the End Times.
Other changes I think are needed
Malekith is NOT Asuryan's chosen. The revelation that Malekith was the rightful Phoenix King all along left many High and Dark elf fans very unhappy because it meant Melekith was right all this time. That being said, many found the idea of all three Elves uniting into one nation quite fascinating. Pity it was never expanded upon as the world was destroyed. In other words, I think Malekith should still become the Phoenix/Eternity King, but in a different way. My idea is that when he does pass through the flames the second time, all other potential canidate for Phoenix King was either dead or unfit to become Phoenix King, and Asuryan has set Malekith on a clean state test. In other words Asuryan is out of better options and is going with what's available... albeit VERY reluctantly.
Plots that went nowhere are expanded upon. Many plots of the End Times were left unfisnished, like Giles Le Breton returning, the three Elf Factions uniting, and Vlad becoming an Elector Count. With Giles, this is a chance for Bretonnia to show the world that it to is a force to be reckoned with despite it's backwards government, and refusal to evolve technologically. For Vlad and the three Elf factions uniting, it could increase tension greatly since good and evil must unite against Chaos.
Lileath is NOT the Lady of the Lake. For many years, it was implied that the Lady was an aspect of Slaneesh, or Queen Ariel in disguise. Many fans were upset when it was revealed that she was really Lileath. Speaking of Lileath, she too received criticism because of the fact that she betrayed and murdered Ariel, and believed that the war was unwinnable. Now maybe her doubts that the forces of Order can win could work in Total War to add tension, but she should not murder Ariel. I dunno what should kill Ariel in the games, or if it even should happen. I know the reason it happened was so that Alarielle could become the Incarnate of Life, and unite the High and Wood Elves, and I think that should stay.
The Forces of Order win. This is obvious for most. I think it should go like this. The final battle is at Middenheim, where you command a united army of Imperials, Bretonnians, Elves, Dwarfs, Lizardmen(Who don't ditch the world like cowards), Greenskins, Ogre's and Undead against throngs of Daemons, Chaos Warriors, Beastmen, Skaven, Chaos Dwarfs etc. Your job is to hold the line for a certain ammount of time while the Incarnates stabilize the rift. At the end, Sigmar gets one final vision, one of Mannfred killing Balthazar. With this, Sigmar is able to warn Balthazar before Mannfred can arrive, allowing the Incarnates to kill him before he can doom the world. After that, with the rift stable, the Incarnates are able to invert it's power, instead of bringing the Realm of Chaos into the world, it sucks it out. Archeon and all his forces are pulled into the portal kicking and screaming, with him shouting that he can't lose. The portal shuts, the Chaos Gods are banished from the world, and Chaos is defeated once and for all.
There's a bonus mission at the end where the Elves lead by Alarielle, and a faction of Tomb Kings lead by Settra take their revenge on Nagash and Arkhan for stealing Settra's throne, and murdering Aliathra.