I agree we'll see more goals from Berbatov and Rooney. But the most they've scored in a premiership season is 15 goals and 16 goals respectively. We're going to need a lot more than that just to make up Ronaldo's 18 league goals, let alone the fact he scored 6 "important goals" which is twice as many as any of our other players last season. So Berbatov and Rooney will have to help make up the goals, not just against mediocre opposition but against the best sides too and that makes the task obviously much harder.
We can also expect a few more goals from a few other outfield players and more goals from Macheda and Welbeck... But the problem is, its likely that only 2 of Berbatov, Rooney, Macheda and Welbeck will be on the pitch at any one time - so if Macheda and Welbeck are scoring a few goals, it probably means its at the expense of Berbatov or Rooney's time on the pitch. So having less time on the pitch than they could means they are less likely to match their best totals, if you see my point.
I personally think we're in dire need of adding a "clinical element" to our side before we do anything else. Someone we can count on to be in and around our top scorers next season and make the difference in every couple of tight matches. That doesnt have to be a striker, but obviously thats where theres the greatest pool of clinical players to choose from. Its hard to find a player that will be able to play two roles, one as a quality winger and one as the club's top scorer... As I said though, if this player was to be playing it would probably mean that one of Rooney and Berbatov would then be off the pitch. So you have to account for that.
The whole job of replacing Ronaldo is... Just impossible. For this season at least. The best we could hope for is something like signing Benzema and Ribery - who even together wouldnt provide what Ronaldo did. But in a couple of seasons, always improving as players, we could end up in a stronger position with those 2 players than the 1 we lost. Or - we could make "the next Ronaldo", which I truly believe is the idea with Ljajic. But of course it took a number of years to create the first Ronaldo and Ljajic will be a work in progress for many seasons too.
We're clearly going to be in a weaker position heading into next season no matter how you look at it. But if we invest the money from Ronaldo's sale into a couple of players, as long as they are the right players with the right characteristics, we can win the league and still give a decent account of ourselves in europe. Though I think we've kissed goodbye to our chances of winning the champions league again in the next season or two. After that our young stars might be ready to deliver on that stage.