We can’t tell if your tamagotchi is going to die or not. They can’t die from low weight. The only way we can tell if your tamagotchi is going to die is in first hand. But you should be able to know on your own if it’s going to die . Your tamagotchi youth does not effect if it’s going to die in the future. However from what I heard Babies can’t die.
Just watch your tamagotchi a lot, play games, feed it, and take good care of it.