For the most part, every Christian agrees that outside the Church there is slim chance of salvation. What we don't agree on is exactly what the term "Church" means.
I've heard compelling theories that the 144,000 mentioned in Rev. 7, the "144,000 Sealed", are Jews who make it into heaven the "old fashioned way." That is to say, they worship the Father alone with no regard to the Trinity.
Said theory goes on to say that we Christians represent "The Great Multitude in White Robes", also of Rev. 7.
However, that same 144,000 is mentioned again in Rev. 14 and Rev.14:4 says that "They follow the Lamb wherever he goes."
The Lamb is obviously Jesus, which is what makes me skeptical of this concept.
The usual counter to that is "Tribulation Saints" and such.
Well, it can make for an interesting discussion.