In a parallel universe where the character Maximus from the movie Gladiator was real and became the emperor after he killed Commodus, and married Lucilla, and adopted her son as the Caesar. For fun, let's assume Maximus wanted to complete where M Aurelius left with the Marcomanni war, and not only that, he and his adopted son Lucius both went full JC on the Germs and brought them under Roman rule for the next 100 years! Roman Empire in 210 AD (Maximus never had children as he never got over with his deceased family). After Maximus died naturally in 235 AD, Lucius becomes the emperor, but unlike his father, he mainly focuses on the empire and not campaigns (similar to Trajan and Hadrian). Due to newfound wealth and slaves, the economy goes up, and so did the silver content of the denari (70% to 90% ). As a result Severan dynasty never happened and what do you think will happen in this case, things like the year of six emperors, 3rd-century crisis, etc. IMP CAESAR MAXIMVS AVG CLEMENTIA- goddess of Mercy
I suppose it is fun to play 'what if' but I suspect that, in this case, Maximus would have been killed by the Praetorian Guard and Septimius Severus would have stepped in to avenge him. Had Commodus not been killed in 192, I wonder how long it would have been before another plot would have been successful. Augustus was not a job with a secure future. How about this one: Plautianus would have weaseled his way into the regime and married his daughter Plautilla to Lucius who would have been killed along with Maximus because neither was as sharp or ruthless as Caracalla in seeing through the evil Praefect. Fiction allows a twist at every turn.