There are still enough games for Liverpool to make a come back and revive their league hopes for the season. With just 14 games already played in the league this season there are 24 more games to play which should be enough to get back into the game and still finish in top four. I am not so much concerned about Newcastle being in the top four position because I have a feeling they will have a bad form and drop points.
In terms of the number of matches that are still quite a lot, it is still very possible for Liverpool to rise and get a better position. But that doesn't mean the others will be worse because all the teams also want to maintain their current position and try to keep getting up so they won't be easily beaten by any of their opponents. And I don't think anyone can judge right away that a team will perform badly after the world cup. For example like you said for Newcastle.