The book of revelations offers a steep penalty for that.
So the Muslims, Mormons (Latter Day Saints), Druze are all doomed?
Dumb, ok. The way I look at it is that if God can divinely inspire the writings, he can divinely inspire the consolidator of said writings to only include the one's he, God, things should be in the bible. If there are other lost writings, like the dead sea scrolls, they were intentionally inspired to be lost. It's a matter of faith, I hope that if there is a God, which I beleive there is, He leads us all to understand and believe what is correct.
On the muslims, mormons and other non christian belief systems, I think it's up to God.
Then it wouldn't be "The Bible" would it? You'd have to rename it to something else. I suppose you could call it the "LinnielouBible", but not THE Bible.
I wouldn't tempt GOD.
Just as valid as the others