Yes, if they get Klopp, I would be really worried. At the contrary, if they get Ancelotti I don't see them becoming a force.
I don't think that their team is that shit. Sturridge can perfectly play the Lewandovski role, Firminho is around the same quality as Kagawa and can play the exact same role, while Coutinho can be their Gotze. They need someone on right wing, but Blaczkekovski - or whatever he is spelled - wasn't a world beater either. A hard working donkey (see James Milner) can do well that role.
Their defense and midfield isn't great, but I think that with the right coaching they can definitely get fourth this season, and then improve it.
I would say that only Mourinho would be a better manager than Klopp in this league, and even him is going in a lot of trouble. Wenger is so last century and while Pellegrini has a fantastic team, he isn't half the manager that Klopp is. I also don't think that our squad isn't significantly better than Liverpool's (it is better but not with a very big difference) and would take Klopp over LVG every day of the week.