Board Thread:TV Show Discussion/@comment-4708902-20161021003952/@comment-28895263-20161023061939

I don't think that House Lannister is in such dire straits. Kevan was not Tywin's only sibling. Book-content suggests two other brothers, and a sister. (HBO has ignored them, so far.)  Possibly cousins, as well; Tytos was not an only child.

The Westerlands have been pretty much left alone, ever since Robb's abortive attempt to take Casterly Rock. There's every reason to belive that those Lannister kin are alive and well, and ready to take on primacy after Tywin's death. Perhaps they already have: Tywin's children are busy with other things and wouldn't notice if a cadet branch of House Lannister has de facto taken over the Westerlands. The lesser lord that Tywin left as castellan might now be acting Lord of Casterly Rock. Who is there to stop him?

House Lannister's real power, of course, came from Westerland's gold; the mines are now depleted. Or, are they? This as yet unknown Lannister castellan might have been keeping two sets of books: building his strength on Westerland's gold, while reporting tapped-out mines to Tywin.