I think if I were a season ticket holder or lived Liverpool area and got to games regulary then I wouldn't think twice about leaving early if I was disapointed with the game, or had to get somewhere for family stuff "or else" cos there is always the next game.
However I live on the south coast so visiting Goodison is more than just about the game, or the result, so stay until well after the final whistle to just take in the match day experience as next home game I'll be 320 miles away on here following the match day thread.