After Burton et al declare themselves the 'AWOL Germans' in the Beer House and the officers (Burton/Eastwood) are being driven in one car, they signal an escape to each other via the mirror.
Eastwood grabs one guard and shoots away, but Burton in the back is flanked by two more Germans, and we only see the German commander fly through the windscreen?
What happened to the two Germans in the back?
Smith (Burton) in the backseat is flanked by a soldier and the officer, Weissner. Up front is Schaffer (Eastwood) sitting between the driver and another soldier.
Schaffer shoves the guy on his left out of the car. Smith grabs the gun of the guy on HIS left and makes him shoot the driver. The car then crashes, sending Weissner through the windshield.
The unaccounted for German is the one on Smith's left in the backseat. He disappears from the car immediately after the crash, when the only German visible inside with Smith and Schaffer is the dead driver, but he reappears and is seen in the back seat when Smith drags Weissner back to the car, but how he died is unclear.
Hope that helps.
"I mean, really, how many times will you look under Jabba's manboobs?"