Does it really matter much who does the killing blow? Without Naruto, Kakuzu and Pain/Nagato would still be there. Without Sasuke, Danzo, Itachi and Deidara would. Being defeated, trying to kill your opponent by committing suicide, pretty much counts as the same. Only difference is that they wanted a boss death instead of just falling down. Alot of main characters died like that: Kisame, Hiruzen, Deidara, Danzo. If you're really strict with it, barely anyone ever killed anybody in the whole story.