Julien had made up his mind—Charlie had already dragged him into this anyway, and he certainly wouldn't stay as a slave who bemoaned his fate every day.
He had boarded Charlie's ship, and the ship had sailed—he just had to come up with a plan so that he could stay on it without any problem.
After all, the chances for him to become the next Rothschild head or how long he would get to live were banked entirely on Charlie's decision.
If Charlie didn't want him as head, he just had to ask Helena