The goal of surgery in these circumstances will prevent any further damage to the spinal cord and nerve roots. Unfortunately any damage that has occurred up to that point is not gauranteed to reverse - the nerves just have to try and heal themselves over time, usually months - after about 1 year the maximum recovery can be judged. An EMG can give an idea about prognosis and the chances of recovery.
It is unlikely that the cord is retethering or that teh lipoma has grown larger. A lipoma is a benign tumor that has probably been there for a long time.
Other ways to reduce your pain and spasticit should be pursued in the meantime like exercise and physical therapy, judicious use of antispasmodic medications like baclofen, and bladder management
Good luck