I've known two horses who got stringhalt. Both retired from jumping for a LONG time. One jumps very small now, and the other is still in semi-retirement.
Not sure on causes, though have heard that eating dandelion is a cause.
From what i've seen of stringhalt, it's horrible. One of the horses could do barely more than walk, loading on to a float had him shaking all over and took about an hour, a step at a time, and neither horse could walk backward. Really sad...
That's about all I know. I believe horses can recover, but some don't. In NO way would I see a horse with stringhalt as a performance prospect, but thats just me.