In the end, Ryan returned to Earth without even trying to obtain control over Poseidon's domain. It was too dangerous since other Greek gods knew where to find that world, and it was basically the fastest way to find the one who defeated Poseidon.
"It will take a while for a while for the other Greek gods to find the one who defeated Poseidon. As long as I keep that crossbow hidden, I will be safe, but after that…" Ryan crossed his arms and then furrowed his eyebrows.