Even before the old sect of West Mountain showed up, he'd already planned to escape from the moment he saw Cheng haonan. Opportunities were always left to those who were prepared, and Lin Yi was the kind of person who could create his own opportunities even if he didn't have one. Otherwise, he wouldn't have a chance to escape at all.
Condensing the Super bomb was the first step. The second step was to retreat while stalling for time against Cheng haonan. The moment the Super bomb was released, he would use the recoil of the bomb to bounce himself away. This was the most crucial third step!
In comparison, killing Cheng haonan was just a side effect-if it weren't for the powerful recoil of the Super bomb, Lin Yi wouldn't have been able to fly fifty miles away like this.