I feel bad if his system is really bricked, and I know accidents happen, but its pretty common knowledge not to turn the power off on any device in the middle of updating. If it's bricked at least you know Nintendo will fix it.
Is it really that long? That's the bigger problem, not that this can happen but that there's that huge window for where it CAN happen. Hopefully if it's really that long it's NOT that long for future updates, a bit easier to handle a brick on a brand new system, even if it is frustrating to need to send it in and get Nintendo to replace it.
I've been needing a UPS again, perhaps that should've been the higher priority.
You run the risk of bricking any piece of hardware if you're doing something as critical as writing to the firmware. That's why you get messages all the time on the Wii, 360, PS3, PSP, 3DS, and Vita warning you to not turn the power off while it's doing it.