You have stated that you feel the post rapture believers will be on their own when it comes to staying faithful to their belief in Christ as their Lord and Savior. In Revelation (7: 1-9) it says that the Angel of God will put a seal on the foreheads of the “servants of God”. It goes on to show that the 144,000 from the 12 tribes (Jews) were at least part of this group, but then it moves right into discussing the “multitude” in white robes that were “serving God and The Lamb” day and night.
I believe the multitude are the tribulation Saints and that they are being included in the group that were sealed on their foreheads by the Angel of God, identifying them as “servants of God”. Also, I don’t think the gentile Christians during this period would be left to suffer the stings of these demonic creatures of Rev. 9 so they must have the seal. In summary; I believe that the tribulation believers will not be able to lose their salvation. Do you disagree with this?
Rev. 7:1-3 shows the four winds being held back by four angels. Then another angel with the seal of God comes forward, telling them not to harm the land or sea until he puts the seal on the foreheads of the servants of God. Rev. 7:4 says the number of those who are sealed is 144,000 and then Rev. 7:5-8 lists 12,000 from each of 12 tribes of Israel. From this I conclude that the 144,000 are the only ones sealed. This all happens on Earth.
After that John sees the multitude, but they are before the throne of God (Rev. 7:11). That’s in Heaven, and the elder tells John they’ve come out of the Great Tribulation. The Greek word translated “come out of” applies to both location and time. In essence it means they will have been martyred and come to heaven before the Great Tribulation begins. They and the 144,000 are not part of the same group. In the first place the 144,000 are all Jews. The martyrs are from every nation, tribe, people and language.
Your concern for Tribulation believers is commendable but I don’t think it’s consistent with Scripture. Both Rev. 14:12 and Rev. 16:15 indicate Tribulation believers are responsible for remaining faithful. Matt. 25:1-13 confirms this. Eternal Security is a special blessing given only to the Church.