According to Hebrews 6:4-6, apostasy pertains to people who meet the following conditions:

Once enlightened: In Greek, “once” means “once for all” (Gr. hapax). This Greek word is used 11 times in the book of Hebrews, mostly concerning the one-time work of Christ (“once offered”, “once purged”, “once died”). So this enlightening is not something that can happen often. It's the one time enlightening of regeneration. The author uses the same Greek word for enlightening (Gr. photizo) in 10:32 referring to the conversion of his audience, saying, “after ye were illuminated [photizo], ye endured a great fight of afflictions.” In addition, Paul uses the same word in Ephesians 1:18 concerning spiritual illumination of believers. The natural man cannot have this kind of illumination.

Have tasted of the heavenly gift: Tasting is scripture is normally used for experiencing God (“taste and see that the Lord is good...”). Perhaps the gift referred to is the “gift of the Holy Ghost” (Acts 2:38), which would mean that this person was baptized in the Holy Spirit and actively empowered for the advancement of the kingdom.

Partakers of the Holy Ghost: This is similar language as 3:1 and 3:14, which refer to believers as “partakers of Christ” and “partakers of Heavenly calling. The same people are “partakers of the Holy Ghost”. Again, this may be referring to the same thing as the “heavenly gift” in the previous clause.

Tasted the good word of God: We again see the experiential nature of tasting. This perhaps shows some maturity level in the Word of God. David exclaimed, “How sweet are thy words unto my taste! yea, sweeter than honey to my mouth” (Ps 119:103). No unbeliever has this level of appreciation for the Word of God.

Powers of the world to come: This perhaps shows that the individual had either witnessed or performed amazing feats of the Lord.

Based on this synopsis, it is possible for someone who is at a more mature level than a mere baby or carnal Christian to walk away from the faith, without any possibility of return (nor any desire to). We have no reason to believe that this is not a regenerated person.