If PSG are genuinely interested in him, sell him. Rashford would probably do well in the French league, might have more time on the ball, defenders more likely to let him run in behind and less likely to press him relentlessly.
Basic question is: does Rashford want to leave United? If so, get him out, to any club that wants him. We've been carrying him since before the Euros. If he thinks he's better than United, there's the door, pal.
However, if he wants to stay, trigger the 1 year contract extension and see if ETH can turn him back into a real footballer. Sell in January if he's still shit, sell next summer if he's mediocre.
Recently Martial was persona non grata and people were hoping we'd sell him for his meat, and after Ronaldo's antics everyone suddenly wanted Martial to lead the line. A player can bounce back if they have the right attitude and the right coaching. To me it looks like Rashford's attitude is better now, and he's got a great coach, so we might get lucky.