Thanks for your question. First--visit this link to read more about treatment of an assymtomatic cuff tear, which is what you are describing:
http://www.rearmyourself.com/article...0be%20repaired
In general, a cortisone shot may last anywhere between a day or many weeks. This then affords one the opportunity to rehab the cuff muscles in order to appreciate long-term relief. A labral tear is by definition inside the joint, so in the absence of a large cuff tear, I would not expect a subacromial cortisone shot to have any effect on pain that may be related to a torn labrum--the point being that perhaps the labral tear is something that was overinterpreted on the MRI, and not a root cause of your previous symtoms. However, if the labral tear is more consistent with degeneration od the superior labral attachment--secondary to Impingement, then this can be addressed when and if it starts to bother again, as part of an arthroscopic procedure, with either biceps tenotomy, tenodesis, or simply labral debridement. I would not recommend repair, as this may not take away all of your pain.
No matter how large a spur---an arthroscopic resection ("acromioplasty") is always possible if one has the necessary expertise in shoulder arthroscopy.
Bottom line----as long as you are feeling better, you are burning no bridges in holding off on surgery so long as you are not experiencing weakness, which would imply a larger tear.
Please let me know if you have any additional questions.