Before entering the Lord of the Universe's universe, Ling Tian had been determined to self-destruct. If he proved no match for the Lord of the Universe, he would choose to blow himself up. But after speaking with the Lord of the Universe, he changed his mind. It wasn't only because he believed the Lord of the Universe would honor their agreement and safely send his friends and family out. More importantly, he knew the Lord of the Universe would likely stop attacking other cultivators.
Ling Tian had decided to self-destruct because he feared the Lord of the Universe would possess Shen Ming and the others. But after probing the Lord of the Universe in their conversation, he learned that once the Lord of the Universe possessed him, he would be nearly fully recovered, even if not completely healed. More importantly, he wouldn't be able to heal himself by possessing other cultivators afterward. Ling Tian chose to believe him on this point.
It made sense. Ling Tian was the strongest among Chi Xue and the others—not just in realm and combat strength, but also in Origin Bloodline Power. If the Lord of the Universe couldn't recover by possessing him, then possessing other cultivators wouldn't help either. Naturally, the Lord of the Universe wouldn't do such a thing.
Since the Lord of the Universe wouldn't attack Shen Ming and the others, Ling Tian wouldn't self-destruct. Even if Hua Min'er, Fairy Meng Shang, and the others chose to fight the Lord of the Universe to the death after his fall, some of his friends and family would still choose to survive. Having some of them live was better than losing them all.
It made sense. If Ling Tian self-destructed, all his friends and family hiding in his Small World would perish. The same