According to Hebrews 6:4-6 and Hebrews 10:26-29, is it possible for an individual who has been saved and then departs from his faith in a life of sin to be restored to salvation?

A resounding YES! It is possible for a backslider to be saved. Foundational to the gospel is the message of God’s great love for mankind and the hope of restoration through the blood of Jesus Christ. 2 Peter 3:9 tells us that God is “not willing that any should perish, but that all should come to repentance.” The Lord does not will that anyone lose his eternal soul; hence, He works through the convicting power of His Spirit to draw all men to Himself. The invitation given in Revelation 22:17, “Whosoever will, let him take the water of life freely,” extends even to the backslider. The Old Testament repeatedly reveals God’s nature of forgiveness and willingness for the restoration of fallen Israel. While there is grace to live a victorious Christian life, if someone loses his salvation because of sin, hope is not gone if there is a willingness to repent and obey the Lord. Restoration is offered to ALL people.

Let us consider the meaning of Hebrews 6:4-6 and Hebrews 10:26-29 in light of the above truth. These two passages in Hebrews coincide in meaning and interpretation. Hebrews 6:4-6 reads: “For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost, And have tasted the good word of God, and the powers of the world to come, If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame.” On the surface, this scripture might appear that salvation is impossible to people who one time truly experienced the power of God’s saving grace in their lives. Thankfully, study of the scripture reveals a different truth. Take note that the reason given that it is impossible to “renew them again unto repentance” is that they are presently crucifying to themselves Jesus again. How can people be saved if they deny the power of the blood of Jesus? When someone denies the power of Jesus to save from sin, it is impossible to be renewed unto repentance. If someone stops crucifying Christ afresh in his life and accepts the power of the blood, there is a place of restoration and he no longer brings shame on Christ. The scripture is not referring to backsliders but to people who have apostatized and rejected the very atoning sacrifice of Christ Himself.
Similarly, Hebrews 10:26 states: “For if we sin wilfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins.” This scripture alone also seems to indicate that there is no sacrifice for sin for the backslider, but the following verses clarify the meaning. “He that despised Moses’ law died without mercy under two or three witnesses: Of how much sorer punishment, suppose ye, shall he be thought worthy, who hath trodden under foot the Son of God, and hath counted the blood of the covenant, wherewith he was sanctified, an unholy thing, and hath done despite unto the Spirit of grace? (Hebrews 10:28-29). These passages bring further clarity on the subject at hand.
There is no sacrifice for sin except the blood of Jesus. If that sacrifice is rejected as unholy and incapable of bringing salvation, there is no other atonement or sacrifice for sin available. There will be severe punishment for those who have been saved and then rejected the blood of the covenant. The scriptures in question do not teach that the backslider cannot be restored to salvation, but they teach that salvation is impossible to the backslider if and as long as the blood of Jesus is rejected as the means of that salvation. “Neither is there salvation in any other: for there is none other name under heaven given among men, whereby we must be saved” (Acts 4:12). When an apostatized backslider changes his heart and mind and accepts the sacrifice of the blood, God will save him by His mercy and grace.