Many of us get attached to those silly little villagers. You should have seen my reaction the first time my favorite villager died (a sweet little blonde-haired girl named Lala, who was wearing a red and white polka-dot skirt)! Unfortunately, there's no way to determine exactly why all of your villagers died. It's unusual to have them all die suddenly, although we have seen reports of it before. There are several things that can spell trouble for your little people, especially in the early part of the game. A declining food supply and untreated illness are the usual culprits if it's been more than 12 hours since you're checked on the game. The tribe needs more attention at the beginning of the game to help them survive until they've improved their skills and made some technological advances.
I'm going to assume that you didn't have a crash, since you didn't mention anything about experiencing one. Another thing that can kill your villagers is adjusting the system clock on your Palm, but you didn't mention that, either.
You may never know what happened to them, but it's unlikely that you'll experience that again with a new game. One thing you can do to get a starting group of villagers that you like is to keep starting a new game (over and over, if necessary) until you get just the right group of villagers to begin a new game. I do that sometimes, to see if I can get Lala back!
