To be honest, what bothers me the most is that there's no one else there. There are not even bodies or anything of that sort. The place just looks like it was abandoned.
Makes the theory that it's all a dream by one of them in a mental asylum or something similar(maybe he lost mind after she died in an accident and is in a coma) seem more probable. I really don't want this though cuz that would ruin any chance of happy ending for those two.