Yeah, I suppose that could work -- Do you have a Scripture that clearly and explicitly says that once a believer is sealed with the Holy Spirit he will always be sealed with the Holy Spirit?
Because it is HIS ETERNAL LIFE that is given to us, not our life made longer. And eternal means, well, eternal
. No beginning, no end, the Life of Christ IN us, and we are IN Christ.
Once one is IN Christ, they are ALIVE in Christ, because of the LIFE of Christ, which is ETERNAL.
"Because I live, you also will live." (from Jn. 6)
25 Therefore he is able to save completely those who come to God through him, because he always lives to intercede for them. (from Heb. 7)
19 “For through the law I died to the law so that I might live for God. 20 I have been crucified with Christ and I no longer live, but Christ lives in me. The life I now live in the body, I live by faith in the Son of God, who loved me and gave himself for me. 21 I do not set aside the grace of God, for if righteousness could be gained through the law, Christ died for nothing!” (from Gal. 2)
And it's not US who must maintain our position of salvation (new birth, inheritance), but God Himself who guards it for us through the resurrection (everlasting life) of Christ:
3 Praise be to the God and Father of our Lord Jesus Christ! In his great mercy he has given us new birth into a living hope through the resurrection of Jesus Christ from the dead, 4 and into an inheritance that can never perish, spoil or fade. This inheritance is kept in heaven for you, 5 who through faith are shielded by God’s power until the coming of the salvation that is ready to be revealed in the last time. (from 1 Pet. 1)
You can't screw that up! Once you've put your faith in Christ, your inheritance is kept in heaven for you, shielded by God's power!
And the guarantor? God's Spirit Himself:
When you believed, you were marked in him with a seal, the promised Holy Spirit, 14 who is a deposit guaranteeing our inheritance until the redemption of those who are God’s possession—to the praise of his glory. (from Eph. 1)
-JGIG