At the end of the film, Colter Stevens has been transported to the train, where he finally averts the explosion and then stays in the body of Sean Fentress. It appears this is possible because he isn’t killed as Sean, so he isn’t snapped back to his body. If he had failed, he would be dead for good since Goodwin pulls the plug on his body.
But what about the real Sean Fentress? Since the Source Code machine is thought to just tap into the memory of someone already dead, there’s not a lot of moral consideration for Fentress considering the mission (which is also Stevens’ situation). But since Sean Fentress doesn’t die on the train due to Stevens’ intervention, what happens to his consciousness?
In Quantum Leap, protagonist Sam Beckett would be downloaded into someone’s body (essentially) and while he is “putting things right, that once went wrong,” that person would be hanging out with Ziggy and the cigar-chomping Al at the time travel facility.
But there’s none of that in Source Code. Would that mean that Fentress’ consciousness is floating around somewhere forever, or is he simply killed when pushed out of his mind? It’s even more final if they merely swap bodies, with Stevens running off with Fentress’ gal while he dies with Stevens’ veggie body.
– Remington Smith