Len Wein and Garcia-Lopez turn in a great story in DC Comics Presents 24 (Aug 80), which serves as an epilogue to Deadman's run in Adventure Comics.
This story even has a number of panels that flash back to Deadman's final tale, in which he tried to help an old man whose son was working for gangsters. It's a great, very sad piece, which concludes with the old man getting killed. Deadman is still traumatized by his part in it, and wants to give up the ghost, so to speak, and just be allowed to be dead. Rama Kushna has no intention of allowing that, and moves Deadman around, getting him involved in Superman's latest case.
It has to do with a scientist who is dying, and who tried to preserve his life by linking his heart with the core of the Earth. But instead of extending his life, he is now giving the entire planet a heart attack. The guy has a daughter, who has a skeezy boyfriend, who has mob links. The mob boss gets involved, thinking the process could give him immortality.
Superman never actually realizes that he is working with Deadman on this case, even though the ghost possesses him at one point, as seen on the cover. There is enough chaos going on for Superman to deal with. The mob boss dies, but by that point it looks like the whole planet is about to be destroyed as well.
Superman flies down into the Earth's core to stabilize it, while Deadman enters the body of the dying scientist, and by fighting death, keeps him alive. Great art by Garcia-Lopez throughout this tale, which ends with Deadman back to accepting his eternal mission for Rama Kushna.
Deadman returns the following year in Detective 500.