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I'm just curious to know why he/she was there.
To effectively remove him/her from the events of Tamriel. This seems to be the destiny of all Heroes.
Many who set foot in Akavir never, ever return. Let us remember the example of poor http://www.imperial-library.info/obbooks/ionith.shtml.
It is possible that one such as the Nerevarine, guided by prophecy, would find a more pleasant fate there, but I don't expect we'll hear from that champion again. He reminds me, in this sense, of the Blue Wizards from Lord of the Rings. Let me read you a passage and see if you don't also see similarities:
"I think that they went as emissaries to distant regions, east and south, .... Missionaries to enemy occupied lands as it were. What success they had I do not know; but I fear that they failed, as Saruman did, though doubtless in different ways; and I suspect they were founders or beginners of secret cults and "magic" traditions that outlasted the fall of Sauron."
^ Perhaps the Nerevarine, like the Blue Wizards from that other universe, was actually on an important mission and he/she failed, but not in a corrupt or wicked way. This wouldn't necessarily render this person dead - simply unheard from. The Nerevarine may be in Tosh Raka's belly, or the Nerevarine may be in another dimension, or sitting pretty on a pile of gold being worshipped by Akaviri snow demons. I don't know. In any event we haven't heard of any Towers on Akavir collapsing so we can assume Nerevar has not continued his God-killing career.