Hi Sandie,
1. It is my understanding that obedience to the organization leadership remains paramount for JWs. To stray from anything they teach is apostasy. As for why: they claim that their governing body is the spirit-directed faithful and discreet slave from Jesus's parable, and that Jehovah has given them the authority and guidance to provide 'meat in due season.' In other words, without them you cannot properly use the Bible as a guide.
2. The fact that people have used the same book to promote two distinct ideas on such an important point for centuries makes me think that the book wasn't written very clearly. But I will leave it to others to make the actual case for either side.
3. The JW belief is that you must be a member of the organization in good standing in order to be saved when Jehovah begins the war of Armageddon. There is no way to guarantee salvation aside from that. If you were a loyal JW for a long time and served faithfully, but lost your faith just before the end, you will die with the rest of the non-JWs.