It comes down to his ability to reprogram his brain to do the things it used to do. Some injuries can manage that, some can't.
I do have to admit that baseball is such a fast-reactions game that I'm not sure I want to get my hopes up, but the surgery was fully successful, and this kid is a fighter. He's made that clear by how far he's already come.
Besides, you tell him he never will, that might just make him more determined to prove you wrong. When my mom had a cancer that inpinged on her brain, she wound up in a wheelchair, and a doc tried to "bring her expectations down" by telling her she'd never walk unassisted again. Over the course of the year after she was pronounced in remission, she gradually worked her way back up to a walker, then to a four-point cane, then to a normal cane, then to walking around in the stiff, awkward kinda I-had-brain-damage-in-a-motor-control-area manner that you'll know if you've ever seen it, then to getting around pretty normally -- and at least part of it was to prove the doctor wrong.
All the physical talent Westmoreland ever had is still there. I don't honestly know what his chances are to ever tap into it properly, but I'm leaving myself open to being pleasantly surprised on this one.