Most decently made phones will last decades if treated well. Repairs are usually needed for damage than failure. Whether it's cut cord, broken headband or whatever. Relatively few phones fall apart naturally or fail electrically. Of those, some hi-end magnesium frames on odd Denons and Sonys have proven a bit fragile, AKG elastics give out with age, same with pads and other 'consumables'.
Most go on seemingly forever without any problems.