It is very doubtful that Jehovah chose the GB in 1919 as the only channel on earth as they claim. I can only say that God would save honest hearted people in all Jesus believing Churches, the JWs inclusive. Some among the GB might be sincere, and might get God's approval individually. The same with all Jehovah's witnesses and all church goers and church leaders. There is that possibility.
However, their stating that God uses them exclusively, you're the only channel, even makes me wonder if God would ever save any with that mentality. Why? Because that is blasphemy to state that the holy spirit led you to one teaching, and later pronouncing the earlier teaching the holy spirit led you to as falsehood. Even saying that you are God's only channel on earth is bogus. It carries serious consequences if Jehovah truly didn't tell you that. And the reasons for making such a bogus claim is too weak. Sometimes I wonder if these guys think it's a joke.
It is doubtful, and I would have said totally impossible for God to choose a group from among the rest without letting them know that fact DIVINELY. Jehovah would have communicated such either through a vision, miraculous works, dreams, angel appearance, fulfilled prophecies etc. When God did that in the first century, he openly supplied abundant miracles to prove that He has shifted His attention from Judaism to Christianity.
When God chose a prophet, He always makes it's clear to the one he chose.
The WT would have been better had they gone on with providing meeting materials for any group that wishes to get those materials, and not forming another religion. If God has not appeared to you, you shouldn't form a religion without his approval. That would be presumptuousness. No matter how bad the Christianity has become, you can do your worship in your house, and not go as far as forming a religion.
Well, we leave God to judge them, but I can only trust my Bible. There is no reason to even trust them. They have a track record of doctrinal errors. Why trust such a group to define what you believe?