This is kind of a weird idea considering what the ending poem is about(such as how Minecraft is a dream.), but imagine a bad ending poem when you die while fighting the Ender Dragon. Discuss.
There already is a short poem for the bad ending, goes like this:
Something along the lines of the poem that we have now, but in this one the beings say that the "Player" is now doomed to live in this world forever,never to wake up, never to escape the dream.