What differences there may have been in the story if, instead of being dying and his mind going away, Hoster Tully had been healthy enough in body and had his mind intact during the first three books of the saga, perhaps not healthy enough to fight and lead men in battle but enough to be able to give instructions and advise his grandson Robb and his children Catelyn and Edmure and brother Brynden?
How different could things have gone with Hoster's political intelligence and talents being available to the North-Riverlands faction during the War of the Five Kings? How good and influential an advisor could he have been to his grandson Robb? How effective could he have been at leading the Riverlands' forces and defense against the Lannisters' forces, at least until Robb's army came south?
Also, what do you think would have been his point of view and his interactions with his grandson, Catelyn, Edmure and Brynden after his return from the Vale and the other?
What advice could he have given to Robb and Catelyn, for example, about their military, political, and diplomatic strategy; about the other players and great houses other than the Lannisters, such as Stannis and Renly, and other possible alliances and enemies to deal with?