The majority of Frozen Shoulders do not have a significant injury. As such, once the capsulitis (inflammation of the capsule) settles, pain improves and motion returns. Unfortunately, the recovery can be hard to predict. A few of my patients have decided to wait a year or two, and their shoulder has completely improved.
Any surgical or invasive procedure carries risks. Before proceeding, you should seek a second opinion from an appropriately qualified health practitioner.