The man in the wall CANNOT be a thing we defeat

[Radio10-O]

in order to keep the mystique and quite honestly the horror of the man in the wall alive, even after the end of the story, we cannot ever be rid of the man in the wall.

He/she/it needs to haunt the Tenno from the background forever, or else it'll feel like a cheap one-off villain. please DE, no matter what, make the Tenno live with the consequences of their actions, whether glorious... or tragic. 

[Bao]

I think the MITW is more a benign entity than a villainous one at this point..

[Nesodos]

I don't think he is a villain.

He seems like the materialised entity of the void that plays around with us because of pure boredom

[Gweredith]

I see him as the Outsider from Dishonored. A very powerful void entity that isn't the void itself and whose powers we can outgrow. However, if we reach the point where we can be powerful enough to defeat someone like him, what else would there be to stop us. So yea, I'd like to have him invincible, too; even though there has to be some lore way we could manipulate the void energy to weaken him.