He's been the best we've found in recent years at playing that position. We've spent a lot of money to come to that conclusion and still have much of the detritus on the books to show for it; Besic, McCarthy, Schneiderlin. He's played well as a foil for Gomes this season. All positives.
However. If he wants to go to PSG (as you'd expect him to) and if PSG want to spend silly money, then we need to take it. Especially if the trust is placed in Brands to find a replacement; be that now or be that in the summer.
I'd like to think that the same James McCarthy who covered every blade of grass for Everton when Martinez signed him is still there - probably not though. But even if plays and has a couple of decent performances it will make him more appealing to other potential suitors.