2 Peter 2:1 "But false prophets also arose among the people, just as there will also be false teachers among you, who will secretly introduce destructive heresies, even denying the Master who bought them, bringing swift destruction upon themselves."
Acts 20:17,28-30 "And from Miletus he sent to Ephesus and called to him the elders of the church." ... "I know that after my departure savage wolves will come in among you, not sparing the flock; and from among your own selves men will arise, speaking perverse things, to draw away the disciples after them."
1 Timothy 6:20-21 "O Timothy, guard what has been entrusted to you, avoiding worldly and empty chatter and the opposing arguments of what is falsely called "knowledge"-which some have professed and thus gone astray from the faith."
Yes, If a Christian starts to believe and practice false teaching, he will lose his salvation.
These false teachers were never Christians to begin with
|denying the Master who bought them [with Jesus blood] 2 Peter 2:1|
|bringing swift destruction upon themselves [formerly saved] 2 Peter 2:1|
|elders of the church Acts 20:17|
|from among your own selves [elders] men will arise Acts 20: 28-30|
|gone astray from the faith [left faith they embraced] 1 Timothy 6:20-21|
These false teachers were at one time bought with Jesus' blood
These false teachers were never saved