The Facial Rig is built using Blend Shapes, and as of now there's no way to export those from UE4 to any DCC, because Blend Shape export is not supported.
To solve this issue, I created a proxy rig within the skeletal hierarchy of the character, adding 52 joints, each one named after each blend shape.
In UE4 I get each blend shape value ( 0 to 1 ) and that value is driving the proxy rig joints on the Z axis.
When the skeletal hierarchy is recorded using Sequencer Recorder and exported to Maya, I then use SDKs to link the proxy rig joint values to each blend shape, in order to drive them in realtime.
The result is a Full Body Motion Capture performance recorded inside UE4 and exported to Maya, including the facial animation as well.
Facial Animation Pipeline - UE4 to Maya