The Second Prince did not find the Immortal Herbs that could extend one's lifespan in the East Sea.
But this did not affect his plan.
If he could find the Immortal Herbs in the East Sea and prolong the Emperor's life, his own stature in the Emperor's heart would rise, and he might even surpass his elder brother and be designated as Crown Prince.
If he failed to find the Immortal Herbs, it would still be fine, since the Emperor would see his filial piety. Compared to his elder brother, who did nothing, this was still a point in his favor.
Besides, going to the East Sea was truly dangerous, with the battle between two Immortals in the Dragon Palace. A slight repercussion and he would have died an untimely death. Having gone through such a perilous situation, the Emperor could not possibly remain indifferent.
Therefore, whether he found the Immortal Herbs or not was not important. What was important was that he had gone to the East Sea.