@MrDidact Some questions for you, good sirah!!!!! So, I've been busily doing some deductive research and reasoning, so anyhow, I wanted to bounce some ideas and propositions off of you. So, according to cannon based off the books, certain Crownlands Houses rose in rebellion against House Lannister/Baratheon when Stannis stated that Robert had no true born heirs from Cersei. Specifically Houses Chyttering, Farring, and Follard. All three houses suffered heavy losses at the Battle of the Blackwater, and then would have been wiped out completely after Stannis's loss at the Battle of Winterfell, with few if any survivors. We know from the books and the show Cersei is completely merciless, as well as House Lannister's history of completely wiping out entire families. ((Houses Tarbeck and House Reyne))
Coupled with these Houses, are the Houses that make up the High Lordship of Blackwater Rush. Houses Thorne, Mallery, Cressey, and Chyttering comprise the region known as the Blackwater Rush, with House Thorne having the High Lordship. ((Rayonet, Chyttering Brook, Mosborough, and Byford. The individual sub-regions that make up this area.))
House Thorne had no heirs, and upon the death of its Lord, its lands and titles would revert to the Iron Throne. House Chyttering is dead, as the First Lord died at the Battle of the Blackwater, then his son, the new Lord, died with Stannis at Winterfel. ((If there were other family members, dependent upon Cersei, Lannister Armies, folks loyal to the Iron Throne, they would have been put to the sword or married off.)) House Mallery, Byford, is led by Lord Tristifer Mallery, who is unmarried, and without issue. His current heir, if he were to die during the reconquest, would have been his Great-Aunt Annara Tristifer, who was unmarried, and 53 at the time of death of Stannis. She'd be very unlikely to be able to make any babies at her age. As for House Cressey, Mosborough, Lord Raynor Cressey leads the house, unmarried and without issue. If he were to die, his titles would revert to his Uncle, Duncan Cressey, unmarried and aged 54. He might be able to produce some heirs, dependent if he didn't die during the reconquest.
Are any of these houses still alive and about, or have they gone extinct? Are their lands currently open/under crown rule, or have had new families placed in rule over these lands? In my post, I am going to have Aerion asking a line of questions along this path, of what lands have no lords/families ruling over them, what problems currently face the realm, bandits, rebels, etc. He is trying to see if he can gain the title to a lordship, if not a High Lordship, though I know/he knows that such rewards would have to hard earned and well fought for. The Blackwater Rush is nice, especially for a new House to start, due to it being on the river, allowing trade, fresh water for farming, and food via fish/aquatic animals. Plus it allows for quick access to the ocean and the world beyond. But far enough from the coast to not have to worry about bad storms, though flooding would be a inescapable thing.