Manchester United should better do away with ten hag, they should shop for a new manager and stop managing a bad situation. Allowing Ten hag to manage Manchester United for the next, is like allowing a bad situation to get worse, he doesn't have the tactical firepower to turn things around for an elite club like United, a manager that couldn't manage an asset like Ronaldo has a long way to go.
As for Rashford, if PSG is coming for him, then he should go, let him try something new on a different ground, he has afforded a wonderful contribution for Manchester United over the years, but given his long stay and the aura within the club at the moment, i don't think he will be offering anything super new to the club because we've seen the best he can offer.
Marcus Rashford doesn't seem to want to go to PSG, because he is aware that there is no tough competition there, but if Rashford wants to be famous in Ligue 1, please go there and it will be easy for him to get it. In the Premier League, Rashford is not as brilliant a player anymore, I mean the same as you that Erik Ten Hag is not capable of developing players. This is because Rashford characteristic of being lazy when combined with Coach Ten Hag is like mixing two types of the same spices in one container.
PSG did receive slightly different treatment because there Enrique was much better than Ten Hag in terms of managing players. Rashford personality can be changed and reshaped into a hard-working player.