What could cause face to flatten in SMAS facelift? Will the face return to normal sometime?

You would need to be seen in person to determine what might be the best solution for you.  Best of luck..

 Hi, I have performed facelifts for over 30 years and have performed many minimally, invasive SMAS facelifts.  In my experience, no facelift technique alone can properly shape all of the "key" aesthetic facial features.  For this reason, I always aesthetically shape the face when performing facelifts in order to make the face more naturally attractive.  If your cheeks are now flat in the front, they will require augmentation to create more shapely cheeks.
 Following my beauty principles, women look the most feminine, youthful and attractive with heart shaped faces.  Heart shaped faces have cheeks that are full and round in the front.  Cheek augmentation with a dermal filler or using cheek implants for a permanent enhancement will create full, round cheeks that will feminize the entire face.
 "Jowls” represent sagging facial tissues and are the main indication for some form of a SMAS facelift.  The underlying SMAS layer, of the face, must be dissected, lifted, trimmed and re-sutured (not merely folded or suspended with threads or sutures that will not last).  The excess skin is then removed and the facelift incisions closed.
My most popular facelift is the minimally invasive, short incision facelift that has all the benefits of more invasive facelifts (traditional, mid-face, deep plane, cheek lift and subperiosteal facelifts) but with these added benefits:
very small incisions and no incisions extend or are placed within the hair.
minimal tissue dissection = less bruising and swelling = rapid recovery ( several days instead of weeks or months with the more invasive type facelifts mentioned)
can be performed in 90 minutes or less, with or without general anesthesia
no incisions within the hair = no hair loss
excess fat can be removed from the face and neck
excess skin removed from the face and neck
cheeks, chin and jaw line can be augmented with dermal fillers (I prefer Restylane Lyft) or facial implants
most patients fly back home to parts all over the world in as little as 3 days post-op
I combine facial shaping with every facelift procedure.  When jowls are present, these should be done in concert and not alone or separately in order to create a naturally, more attractive face.
Hope this helps.