Why do you think Henderson might leave Leighbo? Also, Wijnaldum is going to be a massive impact off the bench for you guys. If one of your other AMs gets injured or is in bad form you won't be losing all that much considering your depth in this position.
I don't see Henderson fitting into the mix really. I think with Klopp liking to play 4-2-3-1, there are better players available in the CM/DM role. Can will only get better and is likely captain material as well. I think that Joe Allen was actually better suited to Klopp's team than Hendo.