For a moment there, I thought Kenpachi spared Nnotoira because Kenpachi found it a fun match (forced to Kendo Nnotoira at maximum power), and Kenpachi would like to resume the fight for another time, another place (just like that time he fought with Ikkaku pre-SS). Turns out he just pities Nnotoira for being a weakass. Nnoitora sure hates himself now, would'nt he?
New threat pops up to confront Ichigo, eh? Maybe it could be Halibel that was seen watching the Ichigo/Grimmjow fight with her companions that decides to mop up on the survivors, or it's Ulqiorra that manages to bust out of Grimmjow's prison earlier than expected. Either way, Ichigo and co. should be fairly screwed, and I don't think Kenpachi has enough stamina to go out for another all-out.