If your spinal cord is severed there’s nothing that can be done, currently.
Depends on how it was severed really... and degree of general damage. Which being said, nerves have been known to grow back to a degree, and we do have stuff we can do now experimental as it may be.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2678281
Some are also in clinical trials... so fingers crossed we get something useful soon.
I did, however, recently see a device they are implanting on severed spinal cords that will pass along the signal. Still in trial phase but hope is on the horizon.
Probably would work great as part of a multi pronged strategy for the worst types of injuries as paired with stemcell treatments. There is also a mtter of how well people respond to given forms of treatment too and in general the sooner a given regime can be implemented the better the end recovery will likely be. So, someone having a relatively fresh injury may respond better to therapy than someone with mountains of scar tissue to work through surrounding that same.
Kind of like with my lumbar spine injuries... when they were "fresh" they would have been categorically easier to treat and deal with than now with all of the junk in the way and the onset of degenerative arthritis due to lack of adequate response therein.