There is no Hard and Fast rule for this. Make shure you do not pull the cables,keep away from children,do not share to people that dont know the value of them.Always keep them in the pouch provided.Dont dump them in tight bags,as I do. The max duration that a pair last me was close to 9 months ( Daily usage). Rest depends on your luck.
This is the reason, the max warranty they provide is 1 yr. The companies are very much sure about their durability.
Only solution, spend money wisely on IEMs with replaceable cables.