Believers in what precisely? And how much belief, under what tests and for how long?
We don't know our future and we judge ourselves in these matters, Jesus does.
Believers are SAVED people. Who believe the gospel of your salvation. That Christ died for our sins, was buried, and rose again the third day. Believers, those who are saved because they believed in the Gospel of Your Salvation, are sealed by the Holy Spirit unto the day of redemption. Not UNTIL, but UNTO. (Eph. 4:30).