Witnesses might say that about Korah, Dathan, Abiram or Ananias and Sapphira, that's true. However their stories was a little more complex than being simply disobedient to Moses or the Apostles.
Regardless of that, while a case could be made that God has used organizational structures over time for his own ends, a person would be on shaky grounds Biblically if they claimed that personal salvation is impossible without being a part of one (the current blessed one, that is), which was sort of the point Jesus was trying to make in Luke chapter 4.
But if that is that case, then modern day Witnesses should speak fondly of the people who become Catholics between the years of 4th and 14th century, as that organization was clearly used by God to preserve the Bible.