We will see if Liverpool really made a mistake by selling Sadio Mane. It is still early to make such predictions about the situation. As I said before, it is depending on how the new trio will play and how Darwin Nunez especially will play in this season. Liverpool got really close to a championship in the league last season but lost their chance by inches. They need to put a bigger effort into it this time to be able to get ahead of Manchester City. They will need to decrease the amount of points lost in easier games to make a difference.
I think Klopp already considering about this and last season Diaz has playing well on Mane position even compare to the performance between these two players for half season i think Diaz very much better so i think that's why Liverpool dare to release Mane especially Diaz salary lower than Mane's salary and regarding new player Darwin Nunez since Suarez leaving the team Liverpool don't have any pure centre striker and i think for next season Liverpool want to change their strategy with makes Nunez as the finisher and Salah and Diaz or Jota as winger so let's see whether this will be effective or not because in the last pre season matches Nunez seems difficult to adapted with Liverpool game