I started having serious RSI symptoms at 19. I was on the computer probably 16 hours a day between my CS program, work, and rec time. My elbows became swollen and painful to the point I couldn't sleep. I took ibuprofen for a while to help, but eventually the amount it took to alleviate pain caused a mild overdose (2800mg in 24 hours is bad juju). Every doctor I went to see told me the same thing - you're going to have to get away from the keyboard. I was fairly certain I'd have to switch careers entirely.

The thing that made the difference for me was paying attention to how I treated my body. You can spend a lot of money to prevent RSI symptoms, but the most important things for me was an egg timer. I started taking 5 minute breaks every 45 minutes to stretch my hands and arms. Now I use AntiRSI (http://tech.inhelsinki.nl/antirsi/) to do the same thing.

The most significant change to equipment was my chair and desk. I invested in a good chair that I could adjust easily - elbow height (and rotation) and seat height in particular. Being at the correct height and angle makes all the difference.

I bought a zero tension mouse (http://bit.ly/HAZYov), which seemed to help with my mousing hand, and had a MS Natural Keyboard at the time. I've since moved on to a kinesis that I like a lot.

Exercise also seems to help - I'm an active rock climber at this point, and it's helped my posture and arm strength.

To the general 'what if you lose function of your hands', I think there's hope. The most important things we do as programmers isn't typing. It's solving problems. If you can still do that and you can communicate those ideas effectively to others, you'll have a lot to offer.