If PSG aren't interested, then I'd imagine Barca will have to reduce their asking cost, or they won't be able to sell them.
I saw PSG linked with Sane the other day, probably crap, but you could see some sort of merry go round with Sane going to PSG and Dembele or Coutinho going to City. I doubt it but you never know.
United could do with a winger so Dembele would make sense for them, and they're probably one of the only clubs that could afford him, but I can't see that happening either.
Basically I think Barca are stuck with at least one, if not both, for this season.