They can still go out if PSG draw. Three teams will have 9 points and the same head to head (if Napoli lose by one goal.) Then it goes to goal difference, which will be equal too. However, Liverpool have scored more goals than Napoli and will go through because of that. This is the most dramatic way for Napoli to go out.
Napoli can lose 2-1 and qualify as long as PSG win. If PSG draw, they will be out. Crazy stuff.
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That's not quite correct. A 1-0 nil win for Liverpool will suffice if PSG win. Any win for Liverpool will knock Napoli out if PSG draw.
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Wait I made a mistake. It's even more complicated.

If Liverpool win and PSG draw, Liverpool goes through regardless because they'll have the most points in the mini head to head table. I don't what the deciding factor will be between Napoli and PSG to advance.