Is your surgery lower only or both jaws? It looks like both jaws are moving in that video you shared.
If it's lower jaw only, Kavan is right that the move will follow the angle of your jaw, which is fairly steep, so it will lengthen and move out.
It's not a matter of 'IF' he's getting only lower jaw 'THEN' Kavan is right.
You must have looked at his video INSTEAD of my astute side by side analytical comparison to say that.
My side by side comparison shows the SAME before and after the doctor gave him which INCLUDES surgery to the upper jaw. It's the same document the doctor gave him that he elected to make some video out of instead of trying to figure out why the chins were on the same level. I also included reference lines that gave the CLUE as to how he confused himself.
Personally, when I see a person does stuff to confuse themselves and then wants their analysis or presentation, thought process -what ever- looked at, I don't bother because it can end up sucking me into their confusion or they just use anything you say as an opportunity to confuse themselves more and then come up with more questions.
So, here, you looked at his video (and not my presentation), it fed into his confusion, he refers back to the video he made where he confused himself and your response to him elicits more questions.
To the OP, lila boy, from my perspective you have ELECTED to CONFUSE yourself and DISREGARDED my presentation aimed at un-confusing you in the process. So, that gives me the signal NOT to address any more of your posts and just leave you to what ever thinking process you want to use to confuse yourself, become more uncertain and/or make your decision.
However, I'll keep my illustration up there in the event someone else wants to spell it out and break down the clue for you.