Jehovah's Witnesses (and others): Doesn't Malachi 4:5,6 somewhat contradict Genesis 8:21?

God never said that there wouldn't be an end to this Earth. He did vow never to again send a flood upon the whole Earth, but He also vowed to destroy the world by fire. There are many references to the Day of The Lord (aka Judgment Day) throughout the Bible. I believe that He was quite upset about having to take 'the breath of life' from man and the other creatures via drowning. When He destroys the Earth with fire, everything will be consumed and there won't be any corpses left, as after the flood.