The separated blade should retain its angular momentum and instantaneously spin like a boomerang about its CG at the same rate as it was rotating when attached. The path of the CG of the blade will instantaneously be tangential to the rotation as the force causing the blade path to curve around the axis of the powerplant will no longer exist.
Over long distances lift and drag will cause the blade to undergo a complex trajectory, but over a very short distance and time, the blade should maintain its orientation and convert some of that angular momentum into lift, much like a maple seed does, though the advance relative to the airframe may not be much in that interval. I'd say that 5 degrees forward is easily a possibility and that armoring a plane against a blade is unrealistic.