With or without lowering springs?
Also, they don't typically fail, they just lose performance over time, so the level of damping that is acceptable to one person will be different than another.
I drive on garbage roads with aggressive lowering springs. I lowered the car at 13k miles and by 25k the stock dampers were garbage. They aren't undrivable, but have lost a great deal of performance.
Other people can go much longer.