Dude, the idea of full avoidance as a DK inside ICC is so far removed from the realm of possibility it reflects a lot of inexperience to have even put forward the idea as a serious talking point. Lich King doesn't just round up your avoidance to the nearest hundred.
It's as Riko said above, you'd just end up gutting your toon's practical application in pursuit of a goofy and unreachable goal.