Difficult to understand what you mean by "flip". The face already goes from 3/4 view in one direction to 3/4 view in the opposite direction. Are you asking to "flip" it as in, the head turns 180 degrees away from us so we are looking at the back of the head?
I just want to know can it be possible to make this present animation with only one front facing sketch.
If I understand you correctly, I think it's up to you how you want to animate the face. If you only need the angles you already have in the video you provided, then you are good. If you are asking of you need us to tell you to have more angles then we can't say - it's up to you. But I apologize because I'm pretty sure I still don't understand what you're asking.
I think he wants to know if the 3D effect of the head turning is real or fake and if so, what trick is used to make it appear rotating having only flat, front facing assets.
Is the OP is asking what the "trick" is, because they aren't the author of that video? I think I was confused because it would seem the OP created that character example. But if it's just an example they found and want to emulate, then I have a couple of videos that explain it ...
Here's a more in depth breakdown where I show 2.5D technbique with a student design and an old version of Flash (2009)
It almost looks like they are using parallax head turns in Adobe Character Animator (CH). Could that be the case?
It is definately parallax technique - easily done in Animate - nbot sure about Character Animator tho. Possibly but not as straightforward I believe.