I think it depends how they replace him.
On the face of it its great as they've lost one of their best players. I 'd say they've sold him for more than he is worth. Ronaldo is a great player but not a better player than Kaka, who went for £65m.
I thought he was fantastic two years ago but disappointing in the first half of last season although he had a better second half of the season. Yet having said that he did score 20 goals from wide which they'll certainly miss. I also think at times he's not a team player- ie Champions League final- apart from behaving like a spoilt child a lot of the time.
So they lose a great player but they have £80m to get a replacement or two.
Unfortunately I think they have the potential to become a better team without him.
Of course another plus though is that they appear to be losing Tevez.
To lose one player when you've got as good a squad as Utd doesnt make that much difference, even if its Ronaldo, but two with Tevez as well, should make it a bit more difficult to keep the continuity going :-)
They also of course have to buy the right players to replace him which is easier said than done.