Well, let's take a look...
Genesis 2:17 But of the tree of knowledge of good and evil, thou shalt not eat. For in what day soever thou shalt eat of it, thou shalt die the death.
It say they will die in that day. No way to discount it.
Then you are actually making God out to be a liar, because Adam did not die that very day, but 900 years later.
Unless God was speaking of a spiritual death. If that's true, then God spoke the truth. Since God is truth, the only consistent understanding is that the death was not physical.
But the Scripture says that God is not a man that He should lie (Numbers 23:19). You have painted yourself into a corner, because if you add to Genesis, the idea that the death must be physical you have only two alternatives:
1. God did not say that Adam was going to die the day he ate the fruit;
or:
2. God lied when He said Adam would die the very day he ate the fruit, when in fact he died 900 years later.
Also, you are saying that God further lied when He said that He was not a man that He should lie, when He actually was lying when He said it! Do you see how adding your new doctrine to Genesis makes everything absurd? You have concluded that God cannot be depended on to tell the truth.
So, how can you know that you are truly saved if God cannot be depended on to tell the truth?