There's only supposed to be 3 or 4 riders that have agreed to compete in Japan, or at least that's what Beattie mentioned on either on RPM or during GP commentary a few weeks back. So it's not really going to jeopardise thier championships though Lorenzo did play a risk game given that he has said all season that he wasn't going to Japan no matter what the risk assesment teams found out. I'm fairly sure all of the riders have it in thier contracts that they are allowed to pull out of any event they choose if they have any safety concerns what so ever, without fear of repercutions. Besides, it would be very hard for Yamaha & Honda to replace proven champions like Lorenzo & Stoner & the companies are not about to sacrifice immediate success over one race meet.