The problem with replacing Suarez is you need to replace the best goalscorer and the best creator in the league. Unless you're taking in Messi, Ronaldo or some such, it can't be done.
I think Markovic and Balotelli are the most direct replacement for him. We'll need at least one of them to hit the ground running, but ok.
I don't think we need a player as good as Suarez to maintain our level though. This team from december/January onwards has been a different unit to the one he came into after his ban. Back then, he came into a decent but not impressive side, banged in two goals a game and basically won games for us singlehandledly. Without that, we'd be much closer to 5th than 2nd last year.
From the second half of the season, he became increasingly less important though, as we started steamrollering the opposition as a team. It become less about everything revolving around Suarez and more about him "just" being the outstandingly best cog in the machine. If we can insert a player or two of high quality to fit as cogs in that machine, I think we'll be grand.
I think the main part to compensate will be players coming off the bench. I imagine there are loads of goals to be made up for by introducing good players in the latter stages of games, as opposed to going down to 10 by introducing Aspas or Moses. And for that matter, being able to do that more often, because it's not Aspas and Moses you have to choose from. With a wider squad to pick from and more quality in for example fullback positions, I think the team as a whole will be able to produce 7-8/10 performances all across the pitch more often than last season.
That, tidying up the defence some more (I don't expect us to be dead solid, just more solid), a few more of our players continuing their progression and I see us improving on our performance from last year. A lot of things to get right, but far from impossible for a good manager. We've got the pieces in, so I'm happy with that. And I think even without getting all those things right, we're still in a very good position for top 4, which I'd be content with.