I have gained 20 pounds since my facelift 2 years ago. When I lose this weight, will my face sag?

One the of the key signs of facial aging is loss of volume.  You can clearly see this comparing infants to the elderly.  As such, any process that causes the face to deflate, ie time, weight loss, or gravity, can increase the appearance of facial aging.  That being the case, all of your weight loss will not come from your face and neck.  If the weight loss does cause some laxity, the facelift can be revised to restore your appearance.  Best of luck

Dependent factors:  How much weight loss?  What is the inherent elasticity of your skin?  Where do the 20# come off your particular body?  Smoke?  Sun?  Quality of the surgery?All the above factors will have some play.  Bottom line is the answer is yes, your skin will show some additional sagging with significant weight loss.  Some more than others.  But you have no choice in the matter.  If you lose the weight...see what happens and if the resultant sagging is unpleasant, I'll bet your surgeon (if he/she has some heart) will give you a super deal on a little touch up.  You'll look better and feel better with the weight loss regardless.  If my patients are going to lose significant weight, I have them at least get close to that weight prior to surgery.