Liverpool's record with Coutinho (6-6-1 & 30-15) in the PL is worse than our record without him (6-1-1 & 20-10) and we didn't win a single match against the Top 6 with him but without him we did beat Arsenal 4-0.
CL record is similar, with (2-3-0 & 20-6) and without (3-1-0 & 10-4).
As can been seen he isn't a critical cog in the machine despite his fine performances overall. Of course I'd prefer to have him, we have a settled attack and integrating a new player (e.g. Mahrez or Lemar) isn't ideal but with one of those two plus VVD I think (hope) we'll be a stronger team overall in the remaining 16 games of the PL.
To take this a step further : If I was put on the spot and asked why our record is better without him (and actually there could be many factors involved and it might not be so simplistic as this) I'd say that we are better defensively as he contributes little to nothing in that regard. Looking at the goals for and against per match over all the matches with and without; with 2.78 vs 1.17 and without 2.50 vs 1.17.
So not much in it, maybe the extra goals come from matches where we have annihilated the opposition ; Spartak 7-0, Maribor 7-0, Swansea 5-0, Bournemouth 4-0, Brighton 5-1 all matches he played and scored in. And I don't think it's a weak argument to say we would have won all of those without him anyway.