I may be in the minority but I believe that signing Ronaldo was a big mistake and letting him leave will prove to be a net positive for the club even without a direct replacement. I say that for 2 reasons:
1. Football has largely moved on from the days of relying exclusively on a point man up top to get the goals. Granted there are still some great 9s banging in goals for their teams (Benzema Lewandowski, Haaland), many teams survive and thrive easily without having the big number 9 up top. Take a look at the Premier League, how many of the best players and indeed top scorers are still number 9s? Salah, Son, KDB, Mane (yeah I know he's gone now), Jota. None of them are 9s. City literally won two titles and dominated the league without a true 9. Yeah I know they went out and got Haaland now but point still stands. Playing without a true 9 can easily be done and we have players with a strong eye for goal in the team (Rashford, Bruno). What needs to improve is the build up play and chance creation. The goals will flow after that.
2. Ronaldo's arrival messed up the form of so many players because of his tactical inflexibility and his subpar link up play abilities. Rashford, Bruno, Martial, Greenwood, Cavani all suffered massive drop offs in form because of his arrival. They were much better before Ronaldo joined and I back them to rediscover that form (Minus Greenwood and Cavani obviously) with greater tactical flexibility and unpredictability in attack going forward. We just need to get the chance creation and build up play part right.