Where are the 7000 in Revelation? OT prophecies? Teachings of Christ?
One verse out of context does not make an exegesis.
1Ki 19:18 Yet I have left me seven thousand in Israel, all the knees which have not bowed unto Baal, and every mouth which hath not kissed him.
One example of an OT witness. What was will be again.
I guess it does if one is following a man who tells them it does. That's the danger of swallowing someone's teaching without doing due diligence - as Paul praised the noble Bereans who DID make sure to determine of what they were being told was so, that it matched up with what Scripture said.
But, whether one believes a fraction of Christians will not apostatize or not, what matters is that the gospel NEVER changes. We are saved by the grace of God through faith and not of ourselves or our works. I imagine the few who fall prey to false teaching on minor issues such as this claim of only 7000 being saved out of the Tribulation, will be pleasantly (I hope) surprised when they find themselves among the countless number of the redeemed in heaven. I doubt it will matter then.