The Dead was a strip by Peter Milligan and Massimo Belardinelli which ran in 2000 AD from prog 510 (February 1987) to prog 519 (April 1987). It is thousands of years in the future. A cure for sickness, ageing and death itself has been discovered. But now a 'subversive' called Fludd must be deliberately killed so that he can be sent to the land of the dead to discover why demons are bursting out of people's bodies.
After his death Fludd met a dead person called Root, who explained that when people die they normally pass through the area of stasis the pair were in to one of the 'Limbo Worlds': "When Earth's population acquired immortality, the demons were able to overrun the Limbo Worlds and use them as a bridgehead to launch an attack... Previously, they'd been contained by Earth's dead, who used special powers, gained on the Limbo Worlds, to combat them." Fludd then travelled to non-human Limbo Worlds where he learned how to fight the demons.
When Fludd tried to pass into the Light Sphere (which may or may not have been his universe's equivalent of Heaven), it rejected him. From a fellow 'Outsider' or 'Limbowraith' he learnt the fate to which he had been condemned: "A creature cannot enter the light through an alien land of the dead. Unfortunately, when a creature leaves his own dead sphere, as you and I have done, they are altered. Their innate powers are increased, but it is impossible for them to return to their own dead sphere... You and I can never reach the Light Sphere. We will stay in the alien dead spheres, feeding on the demons, until the end of time. Fate has stolen our future, Fludd. We are Desolation Angels."
Fludd then kidnapped some dead aliens and forced them to become Limbo Wraiths like him (by removing them from their own dead sphere) so that they could fight the demons. They had an identical 'sister race' elsewhere in the dead spheres, so would hopefully be able to use the dead sphere of their duplicates to pass into the Light Sphere.
The army of alien Limbo Wraiths vanquished the demons. Fludd endured excruciating agony to return to life and kill the people who had murdered him. His entire post-mortem adventure had taken about five seconds. He temporarily imbued some live humans with his power so that they could banish all the demons from Earth, but once they'd done that they were angry to find out that they would then die. They wanted to lynch Fludd but he died (again) before they could get their hands on him.
The story ended with Fludd, the perpetual outsider, wandering the dead spheres for the rest of eternity, looking for a race identical to humanity whose dead sphere he could pass through to enter the light. (On the bright side — no pun intended — perhaps the light was the gateway to oblivion, and owt's better than nowt, right?)
"I wander, I search, dying each minute of loneliness. Only to be reborn, more lonely still. I want answers, I want reasons, I want peace. Dead or alive. It's the same old story."