I was refered to you by Goodqueenaly. “How exactly would Stannis go about repaying the Iron Throne’s debt to the Iron Bank, assuming he wins? Would he “nationalize” the Lannister’s assets as punishment for more or less making Westeros into hell on earth?”

Hi. You’re pretty much on the nose. As Stannis sees it, Cersei cuckolded and then murdered the King, which is treason twice over, Jaime is a kingslayer and a breaker of the King’s Peace, Tywin broke the King’s Peace and then attacked the King’s banner, and the rest of the family aided and abetted. 

So the first thing that happens without a doubt is that the Crown’s debt to House Lannister is cancelled – not defaulted on, but as another form of seizure of assets. That takes care of half of the Crown’s total debt. 

Next, Casterly Rock and its lands and incomes reverts to the Crown. It’s unlikely that Stannis holds it permanently – the Westerosi custom that one person should not have two great seats would probably sway him, as would the difficulty of governing two seats 800 or so miles away. Rather, I’m guessing Stannis would fine the Rock to clear the Crown’s debts to the Church and the Tyrells and the Bank, and then give the Rock to some loyal house. 

But the Rock could easily withstand that kind of penalty. Short of complete confiscation, Casterly Rock is going to be a power in the land, no matter who holds it.