My syrinx is almost wall to wall in my spinal cord. If they drain the syrinx will the spinal cord rejuvenate itself?

HARD TO PREDICT. If your syrinx is creating a compressive effect within spinal cord, risk of future deterioration is very real indeed, and would try to get this under control before more neurological disability ensues. Although you may not necessarily reverse all the pre-existing issues, the likelihood of prevention and cessation of the damage is very good if surgery is performed. Please discuss fully with doc.