Man utd are not really relying on Ronaldo just like they were last season, it's different now, he's not even on the starting lignup of some matches, and they did fine in some of them, in the Europa League they just have to be decent, they don't need to be good against teams like Sheriff and Omonia, second place would be enough for them, it would be easier if Sociedad beat Sheriff though.
This is in accordance with the wishes of the Manchester United team, which is to want to win in every game in order to achieve its target. And it's definitely not just hanging on to someone like Ronaldo. So there is nothing wrong with that because Ronaldo will also be very happy if the team he is in now gets a good performance without him being in the main line-up of the team at this time.