Here is a story I heard from a B-17 pilot.
He was on a bomb run into the heart of Germany. Prior to drop, flying through heavy flak, there was an explosion, and he was momentarily knocked senseless. When he regained his senses, he still couldn't see because the cockpit was full of thick condensation mist. That soon cleared, and he found that the B-17 was in a near vertical climb, from which it did a hammerhead and then started down. He pulled it out of the hammerhead and found that all controls seemed still to be working. He got things going straight and level again, and they continued on their bomb run and dropped their bombs. After that, he went back to survey the damage. Just aft of the cockpit is the radio room, and its walls were completely blown out, with blood and bits of meat all over the place. There had been two people in the compartment who were now gone. Behind that was the bomb bay, and after that, the waist gunners and then tail gunners. Aft of the radio room, things looked OK. On the way back, because they had been knocked out of formation, and with extra drag, they lagged behind the formation and got attacked repeatedly by 109's. But they made it back to base. A month later, they got a letter from a POW camp. It turned out that the radioman had survived. He had his parachute off, but when the flak started to get heavy, he went to grab it. At that moment, a flak hit blew up right inside the radio room. The radioman regained consciousness falling through the air with his parachute still clutched in his hand. He put it on, pulled the cord, and drifted down into a farm, where he got stuck in a tree. The farmer stabbed him with a pitch fork, but the wound was not life threatening, and then he was captured and put into a camp.
Here is a story from I heard from a B-29 pilot.
They were flying over Tokyo on a fire-bombing run. The fires generated such intense updrafts that, hitting one, his B-29 was slammed up several thousand feet and inverted. To get out of it, he ended up pulling through a split S to recover.
I've read stories of Lancasters doing rolls and split s'es, sometimes as the result of overzealous corkscrew maneuvers (which was a standard by which they evaded night fighters) or as a result of hitting strong updrafts from fires.
Also, you can see videos on youtube of B-17's tumbling or doing vertical dives into recoveries. I think that the bombers had a lot of strength. Of course, such maneuvers weren't encouraged, and some resulted in bending the airframe. Some (the ones we didn't hear about) might have resulted in the plane coming apart.
