John 3:16, "For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life." [Present tense]
John 3:36, "He that believeth on the Son hath everlasting life: and he that believeth not the Son shall not see life; but the wrath of God abideth on him." [Present tense]
John 5:24, "Verily, verily, I say unto you, He that heareth my word, and believeth on him that sent me, hath everlasting life, and shall not come into condemnation; but is passed from death unto life." [Present tense]
'death' and 'life' are states of being. One who has passed from 'death' to 'life' (and that 'life' being everlasting / eternal), cannot pass back into 'death'; otherwise, everlasting life was never had.
John 11:25-26, "Jesus said unto her, I am the resurrection, and the life: he that believeth in me, though he were dead, yet shall he live: And whosoever liveth and believeth in me shall never die. Believest thou this?" [ shall . . . NEVER . . . die ]
Romans 6:23, "For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord." [ NEVER ENDS ]
Romans 8:1, "There is therefore now no condemnation to them which are in Christ Jesus, who walk not after the flesh, but after the Spirit." [ NO condemnation - NO damnation ]
Romans 10:9-10, 13, "That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved. For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation. ... For whosoever shall call upon the name of the Lord shall be saved." [ SHALL be - WILL be ]
1 John 5:9-13, "If we receive the witness of men, the witness of God is greater: for this is the witness of God which he hath testified of his Son. He that believeth on the Son of God hath the witness in himself: he that believeth not God hath made him a liar; because he believeth not the record that God gave of his Son. And this is the record, that God hath given to us eternal life, and this life is in his Son. He that hath the Son hath life; and he that hath not the Son of God hath not life. These things have I written unto you that believe on the name of the Son of God; that ye may know that ye have eternal life, and that ye may believe on the name of the Son of God." [Present tense]
The fact remains that if at any time you HAVE (present tense) EVERLASTING / ETERNAL LIFE (and you KNOW it), and at ANY TIME AFTERWARDS you don't have it, then you never had EVERLASTING / ETERNAL LIFE!
If you are promised that you shall NOT perish and shall NEVER die, and then one day you die / perish, then that was a lie! And I'm absolutely certain that Jesus nor His Holy Spirit EVER lied!