Easy, all their mortal followers will have a massive battle royal and attempt to summon all beings involved in this in some form, to Nirn.
Thereby plunging the continent into a massive recreation of the Mythic Era and starting a God War which will make the Dragon War seem tame.
Only for the Dovahkin to undergo an apotheosis and all sides lose.
The Elder Scrolls Adventures: Dragonborn
Review excerpts:
"It's like God of War, only you don't kill Greek gods!"
"I have never played a game that allowed me to do so much deicide in my life!"