Zeph emerged from the rubble in the moon-lit night and drove on towards the nearest place to rest and think of a plan ahead. He was in too much hurry, but first, he had to examine himself and his condition because this was the last chance he got to set things right. He has lost himself once, he can't lose again for his promise, for Queen Anastasia, and most important for his own.
He had to earn back himself by killing Kwastir and freeing Anastasia. He couldn't revive the Naaga tribe, couldn't revive the tree spirit, couldn't fulfill his original promise, so it was the only thing he could do and he was ready to die for it.
He did not wish to redeem for his guilt or sins by doing this as he knew he had to carry them for his life, but doing this would at least give him the courage to bear the weight of those sins. Honestly, he would be much more delighted if he died there but it would not be fair to that little spirit that gave his life for him.