Not necessarily. People always adapt to different technologies. Besides, the facial recognition system should be stellar and it'll render the fingerprint sensor useless.
See, I just can't see how it'll be any better than the system on the Note 7. If not just for the simple fact that you still need to press something to initiate the recognition.... guessing that'll be the new soft/3D clicky on screen home button. So in terms of operation, best case, it replicates the current FPS implementation on the S7. But unless it has a 180 degree field of view, you'll still have to hold the thing in front of your face.
The S8 will be an excellent phone, but the FPS location was a last minute design choice to work around the fact that Synaptics couldn't get the in-screen one working. They just ripped out the heartbeat sensor and threw a FPS in there.... and that sensor is a pain in the butt to use on my wife's S7 Edge.
So yes... I guess you are right... the facial recognition stuff will render the S8's FPS useless, but that has more to do with the fact that the sensor is in a horrible place to start with.