Tywin's death probably lingers longer...like the realm will feel the repercussions far longer than it did when Robb Stark died.
The Lannisters are basically broken as a house, I dunno how you read it any other way. With no Kevan...are there any competent Lannisters left to rule? Jaime can't rule as a member of the Kingsguard and Tyrion has several nagging legal issues waiting for him should he ever return to Westeros. Mace Tyrell is an oaf, but Tarly isn't...I'm guessing Book 6 will be the gradual sweeping away of all of the Lannisters around Tommen with no hope for them unless a new regime takes over and looks kinder on Tyrion and/or Jaime breaks his vows again, which he almost certainly will not do. One of my own little predictions has always been Jaime willingly taking the black in the end, his "shit bucket" honor thing he's always saying to himself and all.