I wonder if it wasn’t some kind of Werner Von Braun deal. The vermin agreed to do some sort of work for us or an ally, and his life was spared?
Rudolph Hess cooperated, and got life. The exact cause of his death (still in prison) at 87 or 93 (depending on who you believe) is in dispute. But it’s a certain fact he didn’t know about or sign off on the Final Solution—and his imprisonment was fairly harsh, especially by modern standards.