There is a rather rare exception or caveat to this biblical concept of falling away vs. backsliding.  I often bring this subject up when discussing the following subjects:

a) Menu-driven, Open-forum Bible Studies:  Menu Items 10 - 16 - 17
b) Minister's Notebook piece, "There is No Second Chance"
c) Bible Study: "Backsliding vs. Falling Away"
d) Sermon:  Moment of Judgment - are we in the time of the ten virgins
e) Minister's Notebook piece, "Condemnation - Questions and Answers"

Invariably when I bring up any of the above-listed subjects, someone will approach me with an account of someone they know who left the church and returned some ten, fifteen or twenty years later.  They often return with new energy and commitment to the Salvation Process and the Work of God.  The question is, "Have these individuals fallen away?"

My answer to this is, "No, they did not lose their salvation by this physical absence and clearly did not fall away."  I say this based on the simple fact they returned to their calling and commitment.  A truly fallen away person would not do this.  Once a person truly falls away, the Spirit of God is quenched.  This, in all but one rare case [creeping in unawares], would not bring them back to the flock.  Indeed, they would distance themselves from the church at almost any cost.

What is going on in these cases of individuals coming back after having physically left for months or years?

For the lack of a better term, I call this the "extended backslide".  Remember that at ANY TIME in a backsliding situation, the firstfruit may repent and once again begin moving forward in the Salvation Process.  Generally backsliding is seen as a purely spiritual situation.  Nothing physically has changed.  Outwardly, everything appears normal.  Generally speaking, no firstfruit can point fingers and say this person is backsliding and this person is not.  It is something between the firstfruit in question and God.  Generally, periods of backsliding are of short duration.  The person repents and begins spiritually moving forward in the Salvation Process.  This sub-process of the greater Salvation Process generally goes unnoticed by the congregation.

In the case of the extended backslider, they physically remove themselves from the church and "seem" to be going back into the world.  There are a number of possible reasons for this.  I will mention two:

1] They were falsely converted the first time around.  That is, they were not being called at that moment they first began to attend church.  They may have been baptized, but they did not truly repent and did not receive the Holy Spirit.  They have now been called and are actually entering the Salvation Process for the first time.

2] For purposes only God can know, He decided to allow a converted person [in the Salvation Process and with the Holy Spirit] to go back into the world for a while to learn some important lessons.  He might also have allowed it to protect this person from someone or some thing [such as apostasy or false doctrines].  Our biblical example of this is the act of disfellowshipping a person.  This is done by the church to bring the person back to the Salvation Process.  Notice this from a letter of Paul:

"This charge I commit unto thee, son Timothy, according to the prophecies which went before on thee, that thou by them mightest war a good warfare; Holding faith, and a good conscience; which some having put away concerning faith have made shipwreck: Of whom is Hymenaeus and Alexander; whom I have delivered unto Satan, that they may learn not to blaspheme." –1 Tim 1:18-20

Paul sent the person back to "Satan" [the world] so that the automatic laws of God, with their automatic consequences would drive the person to repentance and bring him back to the flock and forward movement in the Salvation Process.  In the case of the person who just left, we have a case where the person has disfellowshipped himself and who, after a period of "training," has repented and returned to forward movement in the Salvation Process.  It is essentially the very same process that we call "disfellowship."  The only difference is that one was invoked by a shepherd and the other self-imposed.  The happy result was the same.  The firstfruit returned.  Neither of these two numbered items is a second chance, but rather part of a greater process we call "Godly Calling."

Clearly this is an issue between God and the individual in question.  Neither the church nor the Body of Christ is involved.