Wow, that's a long post, and I'm tired, lol, so will just tackle this one for now.
V21 is relevant here too...
"And you, who once were alienated and enemies in your mind by wicked works, yet now He has reconciled in the body of His flesh through death, to present you holy, and blameless, and above reproach in His sight— if indeed you continue in the faith, grounded and steadfast, and are not moved away from the hope of the gospel which you heard, which was preached to every creature under heaven, of which I, Paul, became a minister"
The "if indeed" serves as confirmation in this case. It's confirming that genuine faith will persevere. It will continue and overcome. The scripture that comes to mind is... 1 John 5:4-5: "For whatever is born of God overcomes the world. And this is the victory that has overcome the world—our faith. Who is he who overcomes the world, but he who believes that Jesus is the Son of God?"
So if you look at the passage, it does not say that perseverance is required for reconciliation. It says first that we used to be enemies, were then reconciled, and then it confirms that the result will be perseverance. True believers will persevere.
Also take note of the fact that believers are no longer enemies....
Romans 5:8-11: "But God demonstrates His own love toward us, in that while we were still sinners, Christ died for us. Much more then, having now been justified by His blood, we shall be saved from wrath through Him. For if when we were enemies we were reconciled to God through the death of His Son, much more, having been reconciled, we shall be saved by His life. And not only that, but we also rejoice in God through our Lord Jesus Christ, through whom we have now received the reconciliation"