Just played through the main quest and….At the temple Vivec mentions the two different accounts of how Nerevarine got killed denying that he himself killed him like the ashlander believes. But in the "Battle of Red Mountain" text behind him there's no mention of how Nerevarine died? Just that the Tribunal eventually broke their oath to Nerevarine and Azura and used the tools to become gods.

The Nerevarine didn't die.

There are conflicting accounts as to what happened to Nerevar Indoril. The Ashlanders and Dagoth Ur both claim the Tribunal killed Nerevar. The Tribunal claims Dagoth Ur killed Nerevar. I believe there may be a third account of Nerevar's death but I don't recall it. Like the fate of the Dwarves it's left ambiguous and will probably remain so. Dagoth Ur maintains his story right up to the very end, of course, but he's also thoroughly insane--hardly a reliable source. The Ashlanders and Dissident Priests weren't there. The Tribunal is obviously going to deny culpability. There is no truly reliable source. In this one instance, however, my money is on Dagoth Ur telling the truth--the Ashlanders and Dissident Priests may not have been there and Dagoth Ur may be insane, but the Tribunal certainly had the most to gain from Nerevar's death and the most ulterior motives for their version of the story. Just my two septims.