[Yogi]

Spoiler:

When Naruto was fighting against Kabuto, the Kyuubi was scared shitless when Naruto was dying. This shows that Naruto's death is something the Kyuubi woul want to avoid.

I don't think the shinobi couldn't defeat Kyuubi because Kyuubi was immortal, it was because one of Kyuubi's nine tails can change the course of mighty rivers.