Well I like Twice but the information we have all points to him being pretty dead.

• Leading up to this we had the chapter establish just how ungodly fast Hawks is, having him basically teleport from in front of Dabi to outside the mansion where Twice was heading.

• Then we have the moment itself where we see Hawks' feather coming in from out of frame behind Twice' neck and the subsequent panel showing Hawks bearing down with all his might and Twice still hasn't noticed the attack.

• Then we see a figure falling from the mansion, presumably Twice after having been skewered through the neck/spine by Hawks' sword-feather.

You are right that this is just a clone dying, because it had the mask on whereas real-Twice didn't. But the implication here is that Twice - the real Twice is dead and/or breathing his last causing any existing clones to die at the same time.

I really like Twice but at this point it would feel like a complete cop-out or serious deus ex machina to have him survive. If Hawks spares him; well that completely goes against everything established about Hawks and his cold, logical commitment to his job. If Hawks doesn't spare him; who the hell managed to out-speed Hawks when he was inches away from the kill?