The in-line engine design has certain operating advantages, as do the V-shaped and the H-shaped and the round-shaped and whatever-shaped engine design out there. However, the design shape of the engine, per se, incorporates nothing magical about it that adds to its longevity.
I remember arguments about the 5.9 I-6 Cummins having a longer design life compared with the 7.3 V-8 International. Yet the manufacturers designed and built them for the same class of usage and the same predicted life before overhaul, and hundreds of thousands of 7.3s in school buses, medium trucks and pickups proved that, and they are still proving it to this day.