While the boy spends his life appreciating all his father did for him, his teenage years were spent realizing one Fridge Horror after another.
"Oh shit, it wasn't really a game. Oh shit, uncle was gassed. Oh shit, Dad was making me laugh with that funny walk though he probably knew what was coming. Oh shit, I can't believe Dad pulled that off."
- A bigger Fridge Horror is the shower he didn't want to take. It was likely the biggest factor that kept him alive.
Guido is still alive
He's alive, survived the Holocaust. The gunshots were just a misfire, and the Nazi ran away frightened. Or maybe it was All Just a Dream. I don't care. HE'S STILL ALIVE DAMMIT.
Guido is actually a Time Lord.
That's why he could pull all those tricks at the first half of the movie. The Camp's Guard Staff were slaughtered in their escape attempt
The US Army showed up mere minutes later. The place was probably surrounded, and having seen other camps, the Army was having none of their shit. Dr. Lessing didn't survive the encounter.