Plaguefall since 10.0.7 is bugged and dosent show in RDF, you have to enter manually in SL timeline. Yes, you can get to them without flying, may die onnthe road to them, but you can go to them.
Also, check dungeon journal for the bosses to see if your class can drop them. Only warr dk and paladins cannot get the trinkets (yes both of them) naturally, they can get them via trading with another char.
from the map the De dungeon is on an island, so can swim over there? thanks