Why does Alleria assume that Locus-Walker is dead when Xalatath comes out of the dark heart?
When Khadgar was getting sucked into the dark heart, he survived by turning himself into pure energy. Locus-Walker is already a being of pure energy. It seems quite possible that Xalatath didn’t kill him at all, but simply traded places with him, making him now trapped inside the dark heart. It won’t surprise me at all if he reappears in the story at some point.
True true, that kind of make sense.
I don’t know if there’s much story value in bringing him back…he’s not a terribly interesting character. I can just see them doing something silly like when we finally get to fight Xalatath as a raid boss, she’ll win the fight and be about to use the dark heart to destroy us, but when she grabs it locus walker will figure out how to trade places with her and trap her inside again. You heard it here first. 
True, quite possible. But probably not. That would be a hell of a cop-out, to do the exact same fake death as Khadgar.
khadgar got absorbed
locus walker exploded and his wraps were everywhere. theres a difference
Khadgar got sucked inside the dark heart. Locus-Walker got nuked into a 100 pieces. Its better to express he got the same treatment as when Varian Wrynn become a huge green nuke bomb when Gul’dan over charged him with the Fel.
Realistically, Blizz can do whatever they want with the story. All we can really do is speculate until or unless something happens.
Would you really put it past this writing team? 
He got turned to ashes. She was very deliberate about killing him and follows it up with doing the same to other people she cares for.
They have an out here though to bring him back if they want. Energy doesn’t turn to ashes. His wraps can turn to ashes, but that doesn’t kill him.