The life tome if fiber cable, barring rats of backhoes, is depenand on the bend radius and any dynamic movement. Other issuses are thermal shock. This has all be calculated and enforce by TELCORDIA. All fiber race ways are made to maintain a minimal bend radius.
Resently, these radii sepcs have change though. Newer sysetems running at longer wavelengyths are supseptable to polarization anomalies which are produced in the fiber during a bend. In short, the bending stess producess non symetrical index of refraction changes.
As long as the above criteria are met, the fiber will last as long as a pice of class, or glass bottle baried in the ground