The words of Saint Paul can help us figure this out.
If there is one individual "temple of God", then it would be the entire population of Christians on Earth.
>Or do you not know that your body is a temple of the Holy Spirit within you, whom you have from God? You are not your own, for you were bought with a price. So glorify God in your body. - First Epistle to the Corinthians, Chapter 6, Verses 19-20
So, a temple does not reside within us, as the believers are temples, but what does reside within each believer is The Holy Spirit, which I assume is what you meant to refer to. Now, who has The Holy Spirit?
>You, however, are not in the flesh but in the Spirit, if in fact the Spirit of God dwells in you. Anyone who does not have the Spirit of Christ does not belong to him. - Epistle to the Romans, Chapter 8, Verse 9
As such, those who believe in Christ as the Messiah--thus belonging to Him--have His Spirit within them. Because you use the word "still" in your question, that implies that these people do already have The Holy Spirit within them, so, really, your question is "Can someone lose The Holy Spirit?" To shift to the words of Jesus Christ, I've come to believe that His Spirit always remains within us from the moment we begin to believe in Him:
>If you love me, you will keep my commandments. And I will ask the Father, and he will give you another Helper, to be with you forever, even the Spirit of truth, whom the world cannot receive, because it neither sees him nor knows him. You know him, for he dwells with you and will be in you. - Gospel of John, Chapter 14, Verses 15-17
However, The Spirit is to be differentiated from the acquisition of salvation, which in my belief, is a lifelong process of "faith working through love" ("working" translated from the Greek word "ἐνεργουμένη," which is basically "impactful work/labor") as Saint Paul describes:
>For through the Spirit, by faith, we ourselves eagerly wait for the hope of righteousness. For in Christ Jesus neither circumcision nor uncircumcision counts for anything, but only faith working through love. - Epistle to the Galatians, Chapter 5, Verses 5-6
Hence, to conclude, I believe that The Holy Spirit does reside in anyone who believes in Christ as the Messiah-God that He presented Himself as, and that The Spirit is always present as a guide back to His will if someone does falter in their faith, but The Spirit's presence as a "Helper" as Jesus describes does not guarantee one's salvation, so if they are unwilling to change, then, to conclude with one more verse of scripture:
>But because of your hard and impenitent heart you are storing up wrath for yourself on the day of wrath when God's righteous judgment will be revealed. - Epistle to the Romans, Chapter 2, Verse 5