The return of John Constantine in Constantine 2 movie arrived far later than the news of most sequels tends to after 17 years, while Reeves himself has had a longstanding desire to reprise the role of the gruff occultist. However, Constantine 2 is intended to continue from where its predecessor left off, the ending of John quitting smoking is something it will need to address head on.
As in his DC Comics stories, Constantine showed John as a chain smoker facing an afterlife in Hell. After John saves the world at the cost of his own life and almost enters heaven, Lucifer (Peter Stormare) cures John's terminal lung cancer in the hopes of ultimately getting his soul. John ends the movie having switched to nicotine gum, showing how much his experience has changed him. As another Keanu Reeves horror movie with a superhero element, this creates a necessary character change for Constantine 2 to follow up on.
While Constantine modified John in a number of ways, most notably changing him from English to American, his chain-smoking is a core aspect of his comic book backstory that the film made into a tool of his character development. Constantine 2 will need to make a key decision in whether John has managed to kick his smoking habit for good when its story begins. This is not simply a matter of carrying over continuity from one movie into its sequel, but the specific circumstances of John quitting were central to his story and growth in Constantine.
Why Constantine Quitting Smoking Was A Big Deal
John spends most of Constantine knowing his death is near due to his terminal lung cancer. Reeves generally embodied a more embittered take on the character compared to Max Ryan's sardonic Constantine on Legends of Tomorrow, but he was a new man by the end. After his sacrifice frees him from going to Hell, he is given a literal second chance with his cancer being removed by Lucifer. Though Lucifer hardly had altruistic motivations for doing so, John still recognizes it as the new lease on life that it is and takes the opportunity for a positive change in his life.
This leaves Constantine 2, which theoretically will take place nearly 20 years after its predecessor, with a big decision in how to handle John quitting smoking, and having John smoking again presents a real problem for his progression. John's chain-smoking might indeed be a staple of him as a character. Despite that, having him revert to the habit again would be a step back for his personal growth.
It might be tempting for Constantine 2 to bring back John Constantine with a cigarette in hand (especially as the possibility of Constantine 2 ing into the DCEU would require him to have a clear character arc after ing the main franchise officially). Still, after his brush with both death and Hell, Constantine ended with John clearly determined to finally quit for good. As a direct sequel following on John's decision to quit, the wisest decision would be for him to stick with the nicotine gum in Constantine 2.
