I give Rafa until half-way through next season. See how progress is and if it's more of the same then it's time to start looking for a new manager. He really shouldn't have made a public "guarantee" late last year about Liverpool finishing top 4 though. For someone who usually guards his words and emotions well, it was a silly think to say. Finding a new manager isn't something the club should rush into, otherwise you become like Chel$ki or Fake Madrid who change staff like toilet rolls and you don't get the long-term stability that teams like Manure or the Gooners have. Finding a good manager who looks like a strong candidate to continue/ build a dynasty at a team is something that needs careful consideration and balancing of the facts, and very little emotion behind it.
Personally I'd like a manager who attracts a few more big name players to the club and isn't afraid to get rid of the pedestrians in the squad. A manager who can bring consistency to Liverpool, something which cost them the title last season. A manager who knows how to win in Europe/ get the team to rise for big matches would be very handy as well.