Well as part of Flames of War’s Siege of Tirisfal event, he’s currently home recovering from torture by the Alliance so he wouldn’t have been at the final battle itself to see events unfold.
That said once he learns what’s happened: he wouldn’t say it in public, but he feels it Sylvanas got what she deserved in losing her capital city after burning down Teldrassil. And he finds it particularly poetic that she decided to just straight up blight it. Alliance holding it is more temporary than blight. However, he’s also partly glad she denied the Alliance the Undercity, as well, because he’s still got to fight in this war and allowing them to have more resources to turn against the Horde would be bad.
Vaknosh Blackwolf's Refuge 