I don't know that I've ever replaced the fletching on an arrow from being worn out, even after hundreds, maybe even a thousand shots. Sometimes the arrow gets lost, one of the feathers will fall off, or it gets damaged. Other than that, I've had fletching get a little frayed on one of the hen feathers, but not enough that I think it affects arrow flight.
I'm not really sure why that is. As a 3 under shooter, I nock a little higher than a split-finger shooter would, and maybe that results in more arrow clearance from the shelf. I try, as I'm sure we all do, to get a clean release, which also helps with arrow clearance.