Not exactly. He ordered one warship to to return there, without letting Akainu know about it. He didn't say what it was for.
And if Marco couldn't fly all the way to his island and needed to take a ride in a boat, then surely Ryokugyu had to do the same. There's no need to fetch dead pirates to prison. I think he thought they were dead or dying when he left them.
And that's why I am worried about King. His race is not that easy to kill, but injury added upon injury, is not that easy to recover from either.
I think he is still in the prisoner mine, because there was a hint that Pluton might lie underneath it. And knowing about Joy Boy, I think he could also know about the ancient weapons, and perhaps even he was the one who suggested to Kaido to conquer it. People were debating a lot if King and Queen were prisoners there. But if my guess is true, they were actually guarding it from invaders, even after Kaido's death.