My wife has a similar (maybe the same) injury sustained from a motorcycle wreck. By the time it was diagnosed (after they dealt with her other injuries) it was too late to reattach it so it remains as is. The other muscles will eventually compensate but there will be certain motions you won't be able to perform or perform well. She still cannot reach into the back seat of the car to retrieve something with that arm. The impact to her quality of life is certainly negligible. She still does yoga, pilates, etc without any issues.