Well, I'd start by reminding you that the Apostles also died pretty violent deaths. You're seeing a correlation where there is none. More to the point, here's what the text actually says:
For I testify unto every man that heareth the words of the prophecy of this book, If any man shall add unto these things, God shall add unto him the plagues that are written in this book:
And if any man shall take away from the words of the book of this prophecy, God shall take away his part out of the book of life, and out of the holy city, and from the things which are written in this book.
First of all, the Lord was speaking to John about Revelation -- a single book in what would many, many years later, become the New Testament. He could not possibly have been speaking of the Bible since the Bible didn't even exist at that time and neither John nor anyone else would have known what He was talking about. More importantly, He was NOT telling John that He was forever done communicating to humanity. He never implied that He was never going to speak to His children again. To insist that He was saying, "I'm done!" is like trying to put a gag order on God.