Interesting question, first let me define my understanding of “conditionalism”. Conditionalism is the idea that when a person believes in Jesus Christ (the conditions are met), and they will live immortality with God. Our eternal life with God depends on the condition of us having a relationship with Jesus Christ. If God has brought us to repentance, and we put our trust in Christ, we have received eternal life, or immortality, but those who reject Christ will also live on forever in what is commonly referred to as hell. This is also what I would consider the “traditional” of life and death within Christianity. A good biblical reference of this can be found in Luke 16:19-31
Conditionalism is normally brought up and is opposed to the view commonly called Mortalism and Annihilationism. This view teaches that upon death the unsaved will be ultimately be destroyed and cease to exist, rather than suffer eternal torment in hell. I believe an error has been made in the understanding of the idea of destruction in the scriptures. Destruction does not mean something is annihilated, or that it ceases to exist. As an example I was cutting some wood the other day. The wood had some old nails in it the completely destroyed my saw blade. The saw blade was no longer of any value to cut wood, so I had to buy a new one. The old one went to recycle….its steel is still in existence some place…it has not completely vanished or been annihilated. To be destroyed or to meet destruction means that something is of no value for the use that it was originally created for.
We were originally created to be in relationship with God. If we do not have a relationship with Jesus upon death, destruction will be our lot in eternal life.
Let’s move to the scriptures that you have brought up. The first is 1 Timothy 6:16. Verse 15 and verse 16 are descriptions of Jesus Christ…referring to immortality, Jesus is the possessor of immortality.
Then Ezekiel 18:20, is part of Ezekiel 18:19-32 in which God is giving a clear message through Ezekiel that each person will be responsible for the sins that each person commits. The sins that fathers commit are not spiritually passed down to their sons and daughters. The one who sins is the one who will die…spiritually. In the New Testament we get the full picture of this; in that without receiving the grace offered through Jesus people will die or face destruction because of their unforgiven sin.
Thanks again for the question, hopefully this is somewhat helpful. If I have misunderstood what you are asking please clarify.