Janus wanted to go with Ryder, but he controlled his urges and stayed behind with his nephew. It was only his powers that were keeping Caen in something similar to a cryogenic state, somehow saving his life for the time being.
He knew that if he left and something happened to his nephew, then it was going to be too late to regret anything at all.
His nephew was already the weakest he had ever been. His life was barely hanging on, and even with everything they could do, it was unlikely that he could be kept alive for more than a short time.
So, reluctantly, he made the difficult decision to stay behind and ensure his nephew's safety, leaving this important task on Ryder's shoulders.
Entering the portal, Ryder disappeared.
***-
Not even the recent security mechanisms established in the Realm of Gods could stop Ryder.
