@Bill
Paul still addressed the offender in question as a brother still, so there is no doubt coming from Paul that he was saved. Look at what Paul testify to the results for excommunicating the offending brother.
1 Corinthians 5:1It is reported commonly that there is fornication among you, and such fornication as is not so much as named among the Gentiles, that one should have his father's wife. 2 And ye are puffed up, and have not rather mourned, that he that hath done this deed might be taken away from among you. 3 For I verily, as absent in body, but present in spirit, have judged already, as though I were present, concerning him that hath so done this deed,
4 In the name of our Lord Jesus Christ, when ye are gathered together, and my spirit, with the power of our Lord Jesus Christ, 5 To deliver such an one unto Satan for the destruction of the flesh, that the spirit may be saved in the day of the Lord Jesus.
11 But now I have written unto you not to keep company, if any man that is called a brother be a fornicator, or covetous, or an idolator, or a railer, or a drunkard, or an extortioner; with such an one no not to eat.
This is why God is judging His House first at the pre great tribulation rapture event in regards to the Marriage Supper. Those saved believers not found abiding in Him, will be excommunicated from that Marriage Supper since churches are not to eat with those brothers living in unrepentant sin.
8 Therefore let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness; but with the unleavened bread of sincerity and truth.
Salvation is not lost but being partakers of the firstfruits of the resurrection in being received as that vessel unto honor in His House ... is that loss. This is where the vessels unto dishonor comes from that did not depart from iniquity before the Bridegroom had come. This is why even former believers are called to depart from iniquity so they will not be denied by Him, but even though left behind as denied by Him, He still abides, albeit too late for the reception of the Bridegroom.
Being received by Him
as that vessel unto honor in His House
is the eternal glory that comes with our salvation in Christ Jesus, for why the call to depart from iniquity in getting ready for the Bridegroom is what that race is all about.
2 Timothy 2:10
Therefore I endure all things for the elect's sakes, that they may also obtain the salvation which is in Christ Jesus with eternal glory. 11 It is a faithful saying: For if we be dead with him, we shall also live with him: 12 If we suffer, we shall also reign with him:
if we deny him, he also will deny us: 13 If we believe not, yet he abideth faithful: he cannot deny himself.
2 Timothy 2:18
Who concerning the truth have erred, saying that the resurrection is past already
; and overthrow the faith of some. 19 Nevertheless the foundation of God standeth sure, having this seal, The Lord knoweth them that are his. And, let every one that nameth the name of Christ depart from iniquity. 20 But in a great house there are not only vessels of gold and of silver, but also of wood and of earth; and some to honour, and some to dishonour. 21 If a man therefore purge himself from these, he shall be a vessel unto honour, sanctified, and meet for the master's use, and prepared unto every good work.
In regards to the apostasy in these latter days where believers believe the lie that they can receive the holy Ghost again, as they are at risked of being damned in being left behind in becoming vessels unto dishonor in His House, ( ( see the risk of damnation in verse 12 ) in 2 Thessalonians 2:1-15 , Paul goes on to the next chapter addressing those that have fallen away from the faith in 2 Thessalonians 3:1-7 and yet when giving the commandment from the Lord to withdraw from them, it was not to treat them as the enemy as if they were not really saved, but because they are saved for why they are to withdraw from them as admonishing them as brothers still because they are still saved.
2 Thessalonians 3:1Finally, brethren, pray for us, that the word of the Lord may have free course, and be glorified, even as it is with you: 2 And that we may be delivered from unreasonable and wicked men: for all men have not faith. 3 But the Lord is faithful, who shall stablish you, and keep you from evil. 4 And we have confidence in the Lord touching you, that ye both do and will do the things which we command you. 5 And the Lord direct your hearts into the love of God, and into the patient waiting for Christ.
6 Now we command you, brethren, in the name of our Lord Jesus Christ, that ye withdraw yourselves from every brother that walketh dis orderly, and not after the tradition which he received of us. 7 For yourselves know how ye ought to follow us: for we behaved not ourselves disorderly among you;
14 And if any man obey not our word by this epistle, note that man, and have no company with him, that he may be ashamed. 15 Yet count him not as an enemy, but admonish him as a brother.
Since Paul still calls them brothers even when having gone astray, you should not assume that Paul was doubting they were truly saved.
