User blog comment:IamJakuhoRaikoben/Chapter 373: Life or Death?, Review./@comment-5840892-20140228175138/@comment-4999650-20140228183416

Hm it's definitely an interesting theory but very unlikely. We've seen them at Fairy Tail at a very young age and they also thought Lisanna was dead for quite some time so I really don't see when they could be going off running a Dark Guild. Especially since Sayla was able to dismantle 2/3's of E.N.D, if they were indeed the Guild Master.