These aren't conditional statements. Rather, they are simply statements of fact. An individual who through an act of the will stops taking part in the pollution of the world aren't subject to the corruption that brings. But that doesn't change their nature. They are simply a cleaner version of what they were before. The proof that their nature hasn't changed is that they return to their former ways. Conversely, those who have become new creations do possess a new and divine nature and will, because of the work of the Spirit walk more and more in the new nature.
Many conflate the actions of individuals with the actions of God. Where God is active, there may be relapses, God has promised His children success...Philippians 1:6.
Also, if the maintenance of salvation is the responsibility of the individual, then salvation is ultimately of works.