Marshall and Tully estimate that during the battle of Midway the Japanese lost approximately 25% of its aircrew from the four carriers deployed. With all four of these carriers destroyed, and no friendly airbases to land at writhing range, how did the remaining aircrew survive? We're they lucky enough to be rescued from sinking carriers or did they ditch in the ocean near other Japanese vessels operating in the area?
Both, although I would say mostly the former. I don't have my copy of Shattered Sword handy, but the aircrew losses as a direct result of the sinkings were relatively low. The majority of personnel losses onboard the carriers were mechanics and/or engineers. There would have been relatively few planes aloft at the time of the sinkings, since both the planes that had bombed Midway earlier and those intended to strike at the American carriers were aboard. It would have been some fighters for CAP plus whatever recon had not yet landed (if any, I can't be sure if there were.)
All things considered, the casualty rates for the carriers really did depend on how roughly handled they were immediately. Kaga and Soryu were the hardest hit, so had the highest casualties of the carriers. Akagi was a slow-motion sinking, and accordingly had the lowest casualties. Hiryu was somewhere in between.
Most of the pilots had to be rescued from the carriers. The Japanese had very few of their carrier-based planes in the air when the Dauntlesses came down, and all of those would have been Zeros on Combat Air Patrol, dealing with the American torpedo squadrons.
This does not, obviously, include planes from the Hiryu, as that carrier escaped the first attack. Thus, her pilots had more possibility to be shot down during the two piecemeal attacks she launched against the Yorktown.