It is uncommon to have C1-2 instability unless you have a syndrome like Downs or Morquios. If you are asymptomatic as it sounds like you are and you do not participate in sports that put your neck at risk (water skiing, snow skiing/boarding, biking, mtn climbing, etc…), then your risk is not high for future injury.
I would think it would be in your best interest for you to get to know a spine surgeon and visit once a year with new x-rays or if new symptoms develop.
Donald Corenman, MD, DC is a highly-regarded spine surgeon, considered an expert in the area of neck and back pain. Trained as both a Medical Doctor and Doctor of Chiropractic, Dr. Corenman earned academic appointments as Clinical Assistant Professor and Assistant Professor of Orthopaedic Surgery at the University of Colorado Health Sciences Center, and his research on spine surgery and rehabilitation has resulted in the publication of multiple peer-reviewed articles and two books.