It's an industry where people leave to go do another studio or make their own. Not that big a deal. Retro Studios hired a number of former Naughty Dog people last few years. That doesn't mean ND is doomed. People just move around. I think this is good for him as he can be free to do what he wants. Willing to bet he still works closely with Sony. We already knew the chance of a Gravity Rush 3 was about as good as well me asking for an Omega Boost remake and Bradlod asking for a Lagoon remake. It was never going to happen.
Bite my shiny metal cockpit!