Meanwhile, Superman arrives on a future Earth, which he mistakes for an alien world. The sun is red, so he is powerless. He finds a car that Toyman sent to the future to try and find water, but evenutally disovers the watchtower crashed on the earth, and sees that all the JL is dead.
It turns out that right after he left, the an ex-Nazi that was granted immortality by a radioactive meteorite (back when he was a caveman) (In an earlier episode he tried to take over Nigeria or something) finds him and tells him he accidently altered the sun, causing the earth to become barren. He helps superman build a time machine, because 30,000 years alone have made him realize being evil is stupid.
Superman goes back and time and stops him from altering the sun, making the world right, and then the JL has to explain that superman isn't really dead. But Batman knew he wasn't the whole time.