I am indeed concerned if Alonso and Mascherano left Liverpool. For me, Mascherano is one of the best in breaking up the attacks and hassle the opponent. The only 1 person i rated higher is Viera in his prime. You need to have the vision to anticipate the opponents' moves, the pace, energy and strength to tackle and hassle the player. I don't see anyone in Liverpool side that can step up. Well, maybe someone like Plesiss will step up but i seriously doubt it.
For Alonso, i actually think he came to Liverpool already a very good player. In fact i think he has lost a little edge in his passing over the last few years. However, that said, he is still the best passer in EPL and cruicial to Liverpool's title challenge. Also, i think he has added toughness, tackling and plays at a faster pace now to make him a more complete player. In the last few years, i think only Xavi can be rated better than Alonso in terms on leading the midfield and spraying all the pin point passes. It is thought that Liverpool may sign David Silva but i don't think it will solve the problem as Silva plays more as a winger.
There is one signing that i think may work, David Villa. Why should we replace Alonso with Villa as some of you might ask? The reason is simple, we have Steven Gerrard. Gerrard, is the best midfielder in the world. Sure, he may not stroke the ball as smoothly as accurately as Alonso but he has the same vision and is more than capable of making the killer pass. Pushing SG back to a creative midfield role may be good as we can switch to a 442 or diamond formation easily. With Villa, we will finally have a top class striker pairing that will rival any teams, Madrid included. All we need to do is to ensure the passes reaches Villa and Torres.
I feel that sometimes liverpool plays too much through the middle and backpass alot. With Gerrard driving the team forward from middle, the 2 wings will enjoy a lot more space and Babel, benayoun, kuyt and Riera will have a field day in crossing or cutting in.
This, i feel is the way liverpool should go as we should play 2 out and out strikers, especially against weaker opponents.