I got stuck on this one last week. The way to get around it is - as soon as the last wave of ghost alts spawn in the back room, run straight back to the start of the instance. Don't wait for the dialogue - the oathbreakers spawn once the dialogue ends. Pass all of their spawn points to where Radanir was. Radanir will spawn at the same time, and you can talk to him, ending the instance, without having to aggro anything at all.
Galadhloth, Hunter 100, Glirithil, Mini 100, Calanor, LM 100, plus lots and lots of alts
Watchers of Elendil ~ Landroval ~ Crickhollow ~ Tarciryan Knights
~~~~ Imladris in the Forgotten West ~~~~