Your premise that none of the Apostles did not write about something that is not contained in the New Testament is an illogical premise.
You do not know that the Apostles did not write about any number of things. Like every Anti-Mormon that has existed, you are not only an Anti-Mormon, you are nakedly anti-logic as well.
You do not know if an Apostle of Jesus Christ wrote a letter to another Apostle of Jesus Christ, unless you have a great deal of miraculous power, the kind of power that only a Prophet or one designated by a Prophet, has.
You are like the Atheists who say that there is no God, and that this is proven by science. When in fact, science does not have the ability to travel everywhere in the Multi-Verse to prove there is no God of the Multi-Verse. And even if that was possible, God could always move to another part of the Multi-Verse, and thus remain hidden. At this time in history, humans have only been able to go as far as the Moon.
So therefor the Atheists who assert that science has proven that God does not exist are completely absurd, and illogical, and are therefor making a false assertion, and have an ax to grind as well. The concept of being able to move between Universes, is only theoretical at this point, no one has actually proven this publicly. Certainly finding and disproving God at this point and time in history by scientists is completely beyond their capability.
But you have made a similarly inescapable easily recognized error in logic. Namely, that you do not have some God-like power to know what letters (or what was or was not written by Apostles) 2000 years ago. You do not have such pretended power. Not you and not any of your Grace-brothers has this kind of supposed power either.
Therefor the premises of your loaded questions is absurd.
Just a thought... Rather than focusing in on certain vague details of the after life, why don't you focus in on learning to keep the commandments of Jesus Christ?
Where did Jesus Christ himself say that by Grace your are saved, so therefor as a result listen to Dark Ages, flat Earth believing, Priests of Tyrants, who lived hundreds and hundreds of years ago... and still you spit out the same Grace Fanaticism that they spewed?
In the day of Judgment what if you are wrong?
What if living Christ's commandments is important?
What are you going to say then?
Hey, I'll do better next time?
There is no next time. There is no second chance. This is it. This is the last chance you have to improve as a person, and to repent like Jesus Christ said to repent. One life is all you get, and you are blowing it, by not concentrating on living the commandments of Jesus Christ.
Just because you believe something is so, does not make it so. (Two and two does not equal something other than four just because you say that it does... no matter how much Satan would argue that two and two equals anything that you want it to.)
Just because you believe that Grace allows you to sin whenever you want to sin, does not mean that that is what Grace allows you to do.
It is the Devils kingdom that allows for Grace.
It is the Devils Kingdom that allows for all manner of wickedness and filthiness to enter in to it.
This is the Kingdom that you and others like you are destined for if you do not repent, and become logical, and become honest, and embrace the truth, and embrace the commandments of our Lord and Savior, Jesus Christ.
Only if you do this, do you have a chance to escape certain eternal destruction. No amount of Grace talk will change that reality. No amount of any talk will change that reality.
Your only chance at redemption is to embrace the truth, and to live the commandments of Jesus Christ with all of your heart, might, mind, and strength.
Focus in on the commandments of Jesus Christ and live them, if you have even an ounce of wisdom in you.