Many people take the sword out and return it right away (depending on how you leave the area, an elf will approach you with a warning, in case you do not see the entry in the quest log). Some take it after all the quests in the Dark Forest are done (assuming they could reload or knew about the killing spree the ghost would go on in advance).
If you didn't finish the urn quest for the collectors, that will be broken, since they are also dead. No critical quests will be broken (the elven council member will not be killed).
Probably not worth the effort, but;
Reviving dead NPCs.
