I shouldn't generalize and say often, but it seems to be often that they're not able to return. I don't have any employment background, but I have a degree in mathematics. After my brain injury, I couldn't add two and two together, and to use a calculator was a problem. Short-term memory most often is one of the problems that follows a brain injury, so to say two plus three plus seven, divided by six...I would forget which numbers I had punched and whether I had punched the “add” sign on the calculator. And to type--and I'm not a good typist--by the time I had looked from the paper to the screen, I'd forgotten what the word was, so I wouldn't be able to type it.
I'm able to add and subtract now. I'm not able to do university-level mathematics, but not many people can. Where I could do it before, I can't do it now, but I'm back to average sort of thing.