The exact meaning of the ending is unclear. It may be implied that Rose, Sharon, and Cybil were all dead from the moment they crashed, and the final scene features Rose and Sharon "returning home." Christopher wakes up from a fitful sleep to find the house empty; the front door is open, but Rose's car is absent from the driveway. However, this scenario is unlikely as Rose's car was found earlier by police, devoid of any bodies.
Alternatively Rose and Sharon may not be dead but instead be trapped in the dream world created by demon Alessa. At the end of the church scene when the cultists are being cut down like wheat Rose tells Sharon to shield her eyes from the horrors (see no evil). Sharon, overcome by temptation, looks into the eyes of the "Demon" (Evil Alessa) in that scene. This fits into the overall concept of movie because the Evil Alessa corrupts the last good part of Alessa (which is Sharon). Afterwords she appears to act strangly, and her eyes seem to "open" as the bridge appears out of town, over the chasm that was there before (almost as if implying that she willed it into existence). The hazy dreamlike cloud (fog) in the "dream" Silent Hill is still present the entire time, perhaps implying that they are still in the dream world Alessa created. This is supported by the fact that there are no people present anywhere after they leave the town. This may also explain why Christopher is able to sense her as if she were just on the edge of reality. Rose and Sharon, despite having left the physical town of Silent Hill, are still trapped in Silent Hill.