Abraham's concern was evident, but he didn't reject the order. He didn't even complain, limiting himself to nodding before descending into the tunnel and closing the trapdoor above him.
Khan closed his eyes, performing the last mental and physical check-ups. He was about to jump into something life-threatening and life-changing, and taking it lightly could very well destroy him.
Khan didn't lack resolve or determination. The meeting with the descendants had only reinforced his desire to grow stronger to silence any attempt to destabilize his authority. That had always been the most efficient way to protect his domain and allies, and he had never feared hurting himself to pursue it.
As for the body, Khan had held back on drinking too much that night, and his glasses always had the plants' toxic substance in them. He wasn't even tipsy, so the risk of lack of concentration or intoxication was non-existent.