Not Dead

If Rean and Roan went all out and worked together, they could put up a fight against a Middle Stage Soul Transformation Realm Zasfin. However, it wasn't just Rean and Roan here. There was also Kentucky! With the three of them together, plus the fact that the Zasfin was completely underestimating them, that brought about their enemy's demise!

In the end, the only thing that came out of that explosion was a broken spear. As for Gater's body, it would be quite hard to find any remains. Of course, Kentucky and the twins didn't leave that situation without any injuries. This was the first time they used it in real combat, and it had to be released at a close distance. With that being said, they were blasted into the Thunder-Fire Punishment Spears.

Yes, what caused the damage wasn't Sun and Moon Obliteration, but the first attack used by Gater, who was already dead. 

*Bang, bang, bang!*