Nat 20 doesn’t just let you do whatever. Cure wounds could easily be interpreted as returning the body to its natural state as the soul percieves it. If wanted his legs back more than anything so much that his soul held onto it like phantom pain, then I would say maybe a Greater Restoration could if he wanted that.
But if he’d grown accoustomed to his new life and his new legs and no longer sought to “restore” anything, having made peace with his injury, then no, greater restoration would just restore him to his own healthy self image. And a spell like cure wounds would do absolute dick.
I’d love to let this play out, narrate the lack of effect of this spell, and kick this asshole from the table.