I've damaged a few bars, but can't say I've every actually "completely" worn one out. I grind the rails now and then, usually don't bother to close them up, and replace the odd tip. Keep the oil up, don't cut dirt, keep the rails true (like chains, a little touch up now and them makes a big difference in longevity).
I get a lot of customers that think they want their bars replaced, and mostly talk them out of it. $18 for a FULL bar grind and tune is a lot better than $50for a new bar.
For some reason, everyone knows about sharpening chains, but most consumers are oblivious of the need for a bar grind. How many of you that ski would throw out the skis when they need the edges and bases tuned?