Continuity mistake: When Chris pulls up at the bridge barricade, he gets out and his collar is down. In the very next shot his Burberry collar is sticking right up.
Continuity mistake: When Rose retrieves her phone from her Jeep, between shots the strap that the phone is attached to suddenly appears around her neck with no motion of her doing so.
Continuity mistake: After the car crash, as Rose walks down the road calling for Sharon, the cut above her left eyebrows disappears for one shot.
Continuity mistake: When Rose arrives at her Jeep to find her mobile phone, her locket jumps into her blouse between shots.
Continuity mistake: When Rose calls for Sharon in Silent Hill, after just arriving, you can see a red car behind her. When she begins running, it is now in front of her.
Continuity mistake: Whe Rose is walking with the lighter, in the basement, the direction of which the lighter lid faces differs a few times between shots.
Continuity mistake: When Christabella drops the dagger, after stabbing Rose in the church, it changes position a few times in following shots.
Continuity mistake: When Chris arrives at the police barricade, the angle of the gates at the bridge changes a few times between shots.
Continuity mistake: When the deformed creature comes out from behind the wire gate, Cybil puts her left hand up onto her gun twice between shots.
Continuity mistake: In the scene where Rose and Cybil are trapped in the small room and Pyramid head is trying to get in right near the end of the scene Pyramid head starts bending the pole. As the angle changes from below to the front, the pole is bent far higher than it was when he first let go of it.
Continuity mistake: When Christopher listens to Rose's message on the phone, she yells "I'm not okay!" however it sounds different to how she said it when we see her saying it.
Continuity mistake: When Anna is explaining what the symbol on the building means to Rose and Cybil, she hoists her bag of supplies over her shoulder. In the next shot, she's gone back to holding it in front of her. Then, over her shoulder again in the next shot.
Continuity mistake: When Rose first enters Silent Hill, she is forced to use a Zippo lighter to illuminate a series of darkened alleyways. However, during the course of the scene, the flame gets larger, to the point it is almost like a torch. While Zippo lighters do have adjustable wicks to make the flame smaller or larger, we never see Rose adjust the wick, nor is there any time for her to adjust it off-screen, as the scene is in real-time.
Chosen answer: They did not die in the accident. Rather, Alessa's rage and the demon's power caused the town of Silent Hill to fracture into at least three different "dimensions" that we know of (the real world, "fog world" and "other world", plus potentially others). Rose and Sharon are unfortunately stuck inside of one of those alternative realities. The sequel also confirms that they are very much alive.