Those whose names are written in the Lamb's Book of Life CAN have their names blotted out. Moses asked God to blot his name from the Book if God would spare the Israelites instead. Our Lord Jesus specifically says that there are those whose names will never be blotted out, thus assuming the reality that some names DO get blotted out.
If St. Paul was referring to people still alive, he was speaking of them as in the state of sanctifying grace. That state, of course, could (and perhaps did) change during their lifetimes. If St. Paul was referring to people already deceased, then he was referring to those whom he could fairly safely assume had died in the state of grace and were indeed included among the elect of God. Whether or not those people had already attained Heaven and the Beatific Vision (with or without purgation first) is unknown and indeed cannot be known in most cases.
Santo, what you need to be VERY careful of is taking passages of Holy Scripture out of their context. Context is NOT just the framework of the immediate written surroundings of a text; Context is much, much larger and more comprehensive than most people realize.
St. Paul's words are his own, and as such have a context within his theological and pastoral teachings. That could be called an orthodox (small o) Christian context.
St. Paul's words are those of an Apostle, and as such have greater weight than those of a layperson or even a pastor of a local congregation. There is, therefore, an Apostolic context to his words, which carry the weight of infallibility insofar as the Holy Ghost inspired the writing of the letters which comprise Scripture.
St. Paul's words (at least THESE words, anyway; we have no idea how many more communications there surely must have been over a lengthy lifetime and ministry) are part of the Canon of Scripture, and therefore have a context for that reason as well. They must be (and are) consonant with the ENTIRE revelation of Scripture.
Finally, for my post anyway, St. Paul's words in Scripture are a CATHOLIC writing, not a Protestant writing or a pan-Christian or pan-spiritual writing. There is, then, of course, a Catholic context (a 'sensus Catholicus') within which his words reside.
I hope this makes private interpretation (of which selective verse-choosing is a definite part and symptom) more clearly dangerous to you. The thing which I have heard referred to as "proof-text poker" is deadly to the life of your soul.
'You have your three verses seemingly supporting X doctrine; I have seven verses that I allege are in favor of the opposite position.' In those instances, those who believe they can make a more comprehensive verse-by-verse case for their (erroneous) doctrines think they have 'won' the argument.
Please refer to a traditional Catholic commentary on St. Paul's writings instead of looking to engender fruitless disputes. Those who are humbly submitted to Holy Church and Her right to own and interpret Scripture should have no interest at all in wresting random verses out of their proper context in order to support heresies of the Prot or any other variety.
St. Thomas Aquinas, faithful teacher of Holy Scripture, pray for us.
Mary, Help of Christians, pray for us.
Most Sacred Heart of Jesus, have mercy on us.