User blog comment:IamJakuhoRaikoben/Chapter 387: Tartarus Arc: Part 4 - Father and Son, Review./@comment-24546844-20140606213817/@comment-24546844-20140607005311

Oracion Seis was in a deserted area somewhere outside Fiore I guess and they don't have a way to go to Magnolia except on foot so it may take some time till they reacha the city

It's just speculation (not even I believe it seriouslyy) but one doesn't exactly cancel the other. Also, rereading the manga I noticed that most of the time Gray mentions his will to defeat Deliora is to avenge his mother and father. You not always avenge something that is dead, in this case he would be avenging what Deliora did to his family, like turning his father into a demon and killing his mom. Maybe a power drunk Silver caused the destructionand not Deliora. The only problem here is that there's no reason for Silver to be the only one corrupted by Deliora as he being a mindless monster wouldn't choose somebody to corrupt but do it to everybody, and, as there are no hints that it happened to anyone before I am deeming this theory implausible.