It is hard to say where you stand from the photo alone. Bone grafts as well as natural bone tend to resorb over time if not used. Sometimes this can occur rapidly and sometimes very slowly. An x-ray and/or CT scan would be needed to evaluate the amount of bone available at this time to support an implant. IF there is not enough bone present, additional bone grafting can always be performed.
Yes, your jaw can be repositioned posteriorly again with a second surgical procedure. But it is extremely possible that there is still a certain amount of swelling present that can distort what your final result will be. I would recommend giving it a little more time before resorting to another surgical procedure.
An anterior open bite as shown in the photos requires surgery as a part of the treatment plan. There is no way to close that open bite with braces alone and maintain the results.
It is hard to tell from the photos you placed, but from what I can see, your jaw line does not look bad. If you are still unhappy with your present profile, a larger chin implant is always a possibility. Orthodontics can alter the appearance as well depending upon what is done. It is also possible to advance both your upper and lower jaws at times if indicated. Liposuction is also an option. Sometimes dermal fillers can be used as well to create better jaw line definition. This form of treatment is only temporary however, and would have to be repeated periodically.
It is way too soon to properly judge your surgery. There is still significant swelling that will resolve over the next few weeks. i would wait a while before judging the result. If you remain unhappy, it is always possible to replace the implant with a smaller one. Don't be too quick to react so that you don't make a change that you are unhappy with from the other direction of not being big enough.
