1- All that "reviving someone is cheap" rant is likely to be Oku's way of telling us "Kurono ain't coming back as soon as this mission ends, got it?"

2- Whenever gantz transports you (the weird rays and stuff), it heals your body. Therefore I doubt Sakata's dying slowly. Back when he said that, he was probably talking about some sort of analysis done to him before entering gantz, receiving the results later