I think unlike a lot of over manufacturers bmw still well over engineer there cars. 100k in this day and age on a big engine diesel isn't much. If its been serviced well it would be as strong as a car half its millage. I think bmw do factor in a high percentage when they design there engines. even the old Vauxhall red top with 150bhp had internals that didn't need changing till 230bhp. you just have to make sure your car is well serviced and with a remap maybe factor in more frequent services. but for reliability a mild map will give you peace of mind and won't do any damage if that's what you are worried about.
Bear this in mind, bmw offer there own power upgrade on most of there diesels, they wouldn't do that if they couldn't take it.