I've had my Deavers for about a year and a half and zero signs of wear. I think most guys would tell you they have zero issues and that the life span will be very long. You could always get them re-arched by any shop if they ever started to sag. I have only heard of them sagging on guys that REALLY beat their trucks up off-road all day every day, and even then, it's as simple as re-arching them and you are all good.
I would also say that the longevity and the durability of Deavers would be light years beyond the stock leafs. Just physics alone, stock leafs are two leafs I believe and Deaver are 9 leafs I think. I really don't think you can go wrong with Deavers. I would honestly say there is a 99.9% satisfaction rating on them around here.