Me too. In my case I got a hint that being on friendly terms with Elven Council supposedly will enable the mindbroken slaves to be restored to normal by the use of a certain potion (follow up of Ancient Neko Statue Quest). Though until now I haven't found any follow up quest related to this restoration potion. Even though I have been taking all quests that will increase friendly relation with Elven Council like Abberation Hunt etc. Oh, I also have assigned Relation Duty to one of my slavers to keep the friendly relation from decreasing as time pass.