I know, I know: There's nothing exciting about watching Cersei sit around with some banker to discuss her credit score. There are dragons torching a Lannister army and we're spending a day hanging out in the Westeros Chase bank. But those brief, agonizing scenes between Cersei and Tycho Nestoris of the Iron Bank could play a major role in the episodes to come.
As one Redditor pointed out, Cersei already made a critical mistake in her dealings with the Iron Bank:
Tycho Nestoris of the Iron Bank said some very revealing things this episode. One was that the Bank does not Bet on winners and losers, it instead invests in the chosen victor. He also says the bank will support the Iron Throne once their debt is paid, not necessarily the current Queen, but whoever is on the throne. Second he appears to be flattering her by saying Tywin never paid his debt in full and she is really outshining her father by doing so. This is her big mistake, Tywin was no fool and he knew that while the Lannisters were in debt to the Bank the Bank had a vested interest in their success. By paying the debt in full Cersei has allowed Tycho to wash his hands of the Lannisters altogether. After what we saw on the battlefield we have a good idea whose position is strongest and who the Bank would like to back. This clearly contributes to the dire situation in Kings Landing with no grain and limited supplies. She will not Abdicate, instead force the dragons to destroy the city at which point the Kingslayer will be the Valonqar most assume he will be. The irony of this theory is in this case the Lannisters are undone by paying their debt.
We just have to assume that Cersei got enough of her gold from Highgarden back in time to repay the debt in full. It's also safe to assume that the Iron Bank only sent Tycho to Cersei after Daenerys invaded in order to get their final payment from Cersei before she's defeated.
What gives this theory weight is that the Iron Throne has operated as a background player in this story for the entire series, from the moment Ned was shocked to learn the Iron Throne was in massive debt. From there, money and debts dictated the Lannister's entire alliance with the Tyrells, which also changed Sansa's fate by marriage. Specifically, in the books, Cersei's mishandling of the debt crisis takes a much bigger role in the main story. It would only make sense that the Iron Bank's final move would be to back the most stable investment: Daenerys Targaryen and her three dragons and two armies.
In other words, Cersei made a bank error not in her favor. Maybe this time, a Lannister should not have repaid her debts.
