[Control rig] bake a skeletal animtion to an incomplete control rig

Let’s say I have a skeletal animation of a human kind mesh in Maya.
And the animation has been imported to UE as an animation sequence.
And for that skeletal mesh I have an incomplete control rig (for example, a control rig with only the left foot controller).
What will happen if I bake the animation to that control rig?
Does all other part of the skeleton’s animation are skiped and only the leg part’s animation get reserved?