I think Lallana will be his "replacement", whether he is the same player anymore or not. Can't really see us signing Keita and another midfielder for some reason.
Then you'd have: Henderson, Milner, Gini, Lallana, Ox, Keita when all are fit for 3 positions (assuming Can goes). Which seems enough?
Craig's reply gives you a good reason why. But ultimately you need to look at those players in terms of roles and likely availability as depth changes when you do so.
We have Henderson as the only player in the group who plays the #6 role. He has had fitness problems since Klopp arrived and, while #6 is his best role in Klopp's system, he is far from being ideally suited to it and is a clear area we could upgrade. Gini has played there a handful of times as an emergency option. It's doubtful that we lose a starting option here in this role and don't replace him.
We have Keita and Lallana as the only two players who offers high level penetration centrally - to link and create for the forwards. Lallana has barely kicked a ball competitively in a year. Keita is a new signing and is likely seen more as 1st choice as the supporting #8 rather than the hybrid #10 role. Plus we were already looking at Lemar last season - a player who shone in this role for Caen & France.
So while listing all the midfielders the club has gives the illusion of good depth, in reality there are 3 distinct roles in midfield and we look a body short in two of them, hence why our midfield has been dysfunctional for most of the season and is certainly the area we will likely see the most movement this summer and also the area where the biggest gains can be made.