I don't see PSG selling him for a reasonable price. Like even if they came to realization they paid too much 2 years ago and for some reason want to sell i don't think they'd just hand him to Barca for like 150M or something.
He is fantastic if he is fully fit but with the way he left, the drama surrounding the whole story, his recent injuries, his dad and friends etc i don't want him back. Only if it was too good to pass on like a swap with Coutinho and Barca not paying that much on top of it but i doubt PSG would accept that. Giving away their biggest star for a player that is pretty much a failure at this point and not making a huge profit off that would make them look silly.