Gallagher looks to be getting a new contract, so zero chance he's coming now. Also he's not the same knid of player as Kamara, Gallagher is more like McGinn, and we're getting McKennie by the looks of it to cover SJM.
Kamara is an awkward one to replace, he's pretty young himself so it's not a case of getting a young player to come in and learnt he ropes. I think we'll see a loan to come in as Kamara replacement then rotation, or as @useless said, some who can replace Luiz AND Kamara, would be an expensive signing whoever it is.