This OP reflects the belief that righteousness is an eternal possession, rather than GOD's imputation and righteous behavior. In other words, the belief that a person can be righteous yet do unrighteous things. But John is clear:
By this the children of God and the children of the devil are evident: everyone who does not practice righteousness is not of God, nor the one who does not love his brother. 1 John 3:10
1 Jn 2:1
My little children, these things write I unto you, that ye sin not. And if any man sin, we have an advocate with the Father, Jesus Christ the righteous:
KJV
This is a third class conditional which should read: And if any man sin [and you can expect that he will]
The point is that while a true believer will not practice sin; he will periodically fall into it.
1 Jn 5:11-12
11 And this is the record, that God hath given to us eternal life, and this life is in his Son.
12 He that hath the Son hath life; and he that hath not the Son of God hath not life.
KJV
Language tends to be quite constant not varying with our beliefs.
1Jn 5:11 informs us that the believer already has eternal life; because God has already given it. This is confirmed in verse 12.
If a person has eternal life at any time; he/she has eternal life ALWAYS or it wasn't eternal while he/she had it!