Those who fall away completely and permanently demonstrate that they were never truly born again in the first place (1 John 2:19).
The verse you use to verify your statement that the person who fell away was never truly saved, I believe you used it out of context.
1Jn 2:18 Little children, it is the last time: and as ye have heard that antichrist shall come, even now are there many antichrists; whereby we know that it is the last time.
1Jn 2:19 They
[the antichrists] went out from us, but they were not of us; for if they had been of us, they would no doubt have continued with us: but they went out, that they might be made manifest that they were not all of us.
Those who fall away because of SIN, EXPERIENCES, OR UNANSWERED PRAY, is not the same as a wolf in sheep's clothing, and neither is it in the same context in which the above verse was written.
Jesus said,
you will know a person by the fruit they produce, as a good tree cannot produce bad or evil fruit, the same as a corrupt tree (ie, a tree that was good at one time and then went bad, like rot that started on a good apple), cannot produce good fruit.
That is what the above verse is about. It is not the same as the below verse, which I believe is how you meant it.
Mat 13:15 For this people's heart is waxed gross, and their ears are dull of hearing, and their eyes they have closed; lest at any time they should see with their eyes, and hear with their ears, and should understand with their heart, and
should be converted, and I should heal them.
Mar 4:16 And these are they likewise which are sown on stony ground
[in the heart]; who, when they have heard the word, immediately received
[it's the same as, agreeing with and believing] it [the gospel for salvation] with gladness;
Mar 4:17 And have no root in themselves, and so endure but for a time: afterward, when affliction or persecution ariseth for the word's sake, immediately they are offended
[and then fell away from believing].
Luk 8:13 They on the rock are they, which, when they hear, receive the word with joy; and these
[words/seeds] have no
[deep] root
[in the heart of the person], which for a while believe, and in
time of temptation fall away [from believing the gospel they heard].
Many Christians believed the promises of God concerning healing at one time, but because they failed to obtain their healing or that of a loved one, they fell away.
Still saved, but fell away from believing the word they heard, which is part of the gospel of Jesus Christ and the work He wrought for us on the cross.
There was an atheist I spoke to who was at one time an ordained Baptist priest.
Both he and his wife fell away because of what he experienced.
The same reason why so many fall away from believing in healing.
He claims to have died 3 times and only saw blackness, and because of that, stopped believing there even what a God.
Again, not the same as a wolf in sheep's clothing.