He also didn't even have his monologue cut short for the right reasons! It's not some kind of "own" on him that Tyrande slit his throat, it's an own on her that he got under her skin, her partial vengeance was unsatisfying, and the trail on Sylvanas is now luke-warm at best. That was gloating. There was no comeuppance. If Nathanos is out of the story for good, it's an unsatisfying way to do it. If he's a future raid boss, they need to nail the shit out of it - but it would also be another weird-ass exception being granted to the character that's undeserved, as Sylvanas is confirmed to no longer give a fuck about him and thus he should be just another Stygia battery for the Jailer to use.
This reminds me of when Dave Kosack said back around Mists that "there will be a reckoning" for Sylvanas and her actions relative to some of the dubious stuff in Cataclysm, and then people insisted that the fall of Lordaeron would be that reckoning after Teldrassil happened, before they knew how it would end. ...then she nuked it on purpose. Now people insist her characterization was all just as keikaku and that she was good all along/a redemption arc is coming. Exciting reckoning if true, guys!