Selling the players they currently have when their performance is declining will be a big loss for Manchester United, because the value of their players will also decrease. But keeping them is also not the right solution, Man United clearly needs a refresh in their squad. So whether they like it or not, Man United must sell their players at a loss and spend their money again to be able to recruit new players who are more promising.
Man United has retained several players for a long time but the results are always the same even though they have changed coaches several times. So it is quite natural that now Man United is starting to change the depth of its team squad on a large scale. So currently even the names of several star players owned by Man United are also on the list of players who will be released when another club wants them. And I think this step has to be taken sooner or later. And yeah maybe now is the right time.
Financial losses resulting from decreased sales value have become a risk that a club must take when its team experiences a decline in performance and this is a common thing.