Tend to agree about Henderson. I think Klopp has even said Henderson is a player that needs to be 100% to be effective and if they're worried the breakdowns are going to continue or become more frequent, I can see them cutting their losses. I also don't think he works really well in a midfield "2," or at least hasn't really with Can. Great to have in a 3 though, because of the motor and when he's on he can be like an extra half player. I don't think he's a good leader though, more of a teacher's pet/good example, and he hasn't developed the impact in the final third that would take him up a level.
I'm a big Lallana fan, I like his style and he's one of the few Liverpool players along with Joe Allen who seem to be able to maintain possession in advanced areas and play around pressure and in tight spaces (not to mention the off the ball work and pressure), but again, in the position he's been playing in Liverpool, he has needed to have more impact with goals/assists/creation. Although, unlike Coutinho/Firmino, when he has a bad game at least he is still buzzing around -- those two just tend to disappear.
But I could definitely see Lallana working well with Kane/Eriksen/Alli. If you think you already have three guys who will get double figures, Lallana could slot in really well.