I wish we had before and after photos to understand whats going on. But important thing is to follow up with your doctor. The options are wait and do facial muscle exercise to get the muscle bulk back or do small amount of botox to improve the balance of the face. The dimple disappeared possibly because of weakness of Zygomaticus muscle that will recover as botox effect wears off. If the botox is given in the lower part of masseter then the facial muscles are spared.
This problem is pretty complex but I will give you my thoughts. When doing simple things like forehead or frown or crows Botox is simple. Botox is simple for underarm, or palm, or foot hyperhydrosis (wetness). BOTOX for facial asymmetry or reduction - balance is NOT SIMPLE. Patients I see who want masseter reduction or correction of asymmetry, I see once every two weeks for 6 or 8 visits. I use tiny amounts of Botox and slowly work to correction. I have many Bell's Palsy patients and stroke patients that I have greatly helped. I have many patients that had broad lower faces that have had pleasing results. The story of success depends on the patients willingness to commit to the many visits along with the associated expense and time of many visits. It is not easy to attain symmetry in a paralysis patient but with many visits I can get them much better. Both the doctor and patient learn what it takes to attain symmetry. Every patient is different. These are NOT SIMPLE BOTOX TREATMENTS. This is a real combination of learning, science, and art. Hope this helps. My Best. Dr C