Hidan, Kakuzu's partner, is still alive and trapped under some rocks. We don't know the full extent of Hidan's abilities other than he's immortal and he can hurt people by hurting himself. He could have someway out of there, and he's literally in Konoha's backyard while Kakuzu is being held in Konoha.
Now to the point... Kakuzu's hearts were destroyed, but his body is still in one piece. And since he's basically just body parts held together by his black thread, I see no reason why Hidan couldn't just walk into Konoha and "find" his buddy a new heart.
Them losing could has also been a plan to get into Konoha without suspicion, that would explain why they were so half-developed and their fight seemed so damn fixed.
Post Edited:2007-10-15 21:34:05