Is bone absorption due to chin implant reversible?

First, chin resorption following the placement of a chin implant is uncommon. Unfortunately, if the implant is removed the bone does not grow back. If this is a major concern, you might want to consider a genioplasty. Good luck

 Hi, I have performed many facial shaping procedures, including Chin Augmentation with dermal fillers or silastic chin implants, for over 30 years.  In my experience "true" bone absorption from a chin implant is quite rare.  I can think of only 1 case in the last 30 years that I've seen this occur.  It's far more likely remodeling of the bone with actual stimulation of some bone to grow around the very bottom of the implant in response to the implant laying on top of the bone.  In either case, this won't reverse itself even if the implant is removed.  The bone growth is rarely a cosmetic issue but a nasal rasp can be used to file down any excess should the implant ever be removed. When the chin is weak, this creates an imbalance making the nose appear larger, the mid face top heavy, the lower face looks short, de-emphasizes the lips and allows early formation of a "double chin".  
 Proper placement of a silastic chin implant adds forward projection to the chin thereby creating harmony and balance to the lower face.  Using the same incision, liposuction can be performed to reduce the fat and further shape the neck.  Excess skin, from below the chin, can also be removed through the same incision.  
 I have found that placement of a silastic chin implant, through a small curved incision under the chin (also allows excess skin removal) to be very safe, quick, highly effective and far less invasive than a sliding genioplasty (requires extensive tissue dissection, bone cuts and placement of metal screws and plates to secure the cut segments of bone).  I perform chin implant surgery in 30 minutes or less, often using a local anesthetic alone.  
Hope this helps.

No. It will not go back to any original shape since it is a scalloping of the chin shape. It may not be noticeable dependent upon the thickness of the overlying muscle