I have few bicycles with internal gear hubs. 2 with 3 speed one with 7 speed. One commuter with a shimano 3 cc coaster brake for short distances, up until 30 km/day, one for long distance commuting bicycle with a Shimano Nexus 7 and finally a mountain bicycle with a 3 speed 333 shimano hub. I had no problem with them, and they never stoped working, independently of riding conditions.
If you take a look around you may notice that Down Hill bicycles are being equiped with internal geared hubs, and you have to agree, that even for short distances, these bicycles are used in extreme impact conditions