You're quite right that people have posited that the world will come to an end by fire or ice. Some have even added a twist to it - that the world will end by flood again.
But let us ask ourselves, will the world really come to an end? Suppose we examine the possibility that the world will not come to an end but that changes, or evolution, will forever continue to happen? For example, we do know and understand from scientific history that the looks, shape, size, etc. of man took a sharp turn for the better when man discovered and started using fire. His diet changed, his living style and abode changed, his power over the elements and the other creatures increased. Fire helped man to conquer the fear of darkness and subsequently dispelled a lot of superstition and ignorance.
Similarly, in another 500,000 years man's looks, abode, etc would be very different from what it is today. That does mean an end to our present lifestyle and possibly looks but not an end to creation as we know it today.