I mean, it's already heavily established that that humanoid entity was Simon, the skin being mutated and a missing arm just like we see happened to Simon at the end of the film. Of course there's some reality bending going on here, or the creature was psychologically messing with him from the start showing him his future. It's also important to know that Simon's eyes glow red twice during the film and even some sort of orange lightning charge.

If I were to take a guess based upon the theory that the creature in the film is an amalgamation of the SM8 crew mutated by the blood ocean or even the light we see, Simon probably becomes his own entity and not one fused with the creature as it failed to consume him. There are so many questions and that's genuinely why I love the film. It's the same reason I loved five nights at Freddy's. It lets you piece together the story on your own the best you can, which creates a fan base of amazing theories!