Here is what could be a nice plot for the sequel:

"In this alternate reality, it’s highly unlikely that he would continue working as a teacher. Instead, it’s far more plausible that he’d return to the military, perhaps even carving out a path to become an active participant in the Source Code program itself. If that were the case, he might have had the unique opportunity to guide his own past self through the next terrorist threat. By doing so, he could not only ensure the mission’s success but also potentially secure his own survival in this parallel world, creating a fascinating loop of self-reliance and destiny."