Gone Elsewhere has the rundown for you. This script meets up with Maximus seconds after he comes to in the afterlife. Our deceased gladiator isn't met by his family, but by a mysterious figure named Moredecai. He introduces him to the Roman pantheon who mock him, and offer a deal to kill their brother Hephaestos. If he can, they'll reunite him with his wife and son. Once out of immortal earshot, Moredecai tells Maximus these are lies and that his wife, Maria, sacrified her place in Elyisium to allow their son, Marius, to cheat death. He's now back in Rome living a mortal life. Disbelieving this, our undead hero marches to find Hephaestos who is trying to usher in an age of a "one, true God" and sends him hurtling back to mortal Rome. There Maximus encounters the adult Lucius who is pretty busy slaughtering Christians for the Emperor, a situation that Maximus finds himself embroiled in ... and not surprisingly, one that reunites him with his adult son. There's the cue to unleash hell.
Needless to say, it's a unique read. Cave really took the "What we do in life, echoes in eternity" tagline literally. (You'll know what I mean when you get to the end.) It's so easy to let your mind get carried away imagining scenes like Lucius passing a bust of Maximus and realizing he just saw him in a mob that I'd like to see this filmed, albeit not as a Gladiator sequel, but as pure Roman fantasy. Read it, and see if you agree.