Im having the same issues... well sorta. At first when i got to white forest, people where their, but i didn't save after entering because i wanted to wait a while to see if more people would come. So after about a week of checking then resetting all of the people that would bring pokemon vanished and it's been about a week since and still no one has returned other than the 2 people walking around the forest to begin with. No grass, no water. Not once did i ever change my DS's clock, nore have i connected with anyone on my game in any way. I have connected to the dream world, tho i can't remember if it was before or after they vanished.(im pretty sure it was before) I heard that the point system for when the people begin leaving doesn't start going down untill you first visit it, so that and the fact that they all suddenly vanished rather than one at a time or so like it seem's to suggest on serebii and bulbapedia is making me think it was probably some kind of glitch, or it's all reset after a certin amount of time and your screwed after that time and no one has realized this.