I'm firmly convinced that the only players in the NHL the Flyers would include Provorov in a deal for are McDavid and Matthews. Obviously, that's not happening, and just as obviously, those aren't the only players in the league whose value would justify a deal in a vacuum, but the opportunity to lock in a #1 defenseman for the next decade (our first home-grown #1 defenseman since Jimmy Watson, IIRC) isn't something we're giving up unless we're getting back a player so insanely talented and marketable that ownership would fire Hexy if he didn't do it.
That's not to say Pietrangelo and Fabbri aren't great players, but Provorov on his ELC is too great a value to give up.
(Also, G's apparently still been recovering from his hip surgery, and hasn't been 100% all year, but that's neither here nor there.)