Dogmeat is the dog companion character in Fallout 3. He's named after the dog companion in older Fallout games, and will be acquired in a similar way.Fallout 3 Wiki: Dogmeat (Fallout 3)

This isn't like most of the other video games out there: most of the time, when people die in this game they stay dead. That holds true for Dogmeat as well. Once Dogmeat joins you, he can die. Once Dogmeat dies, he can't be brought back.Fallout 3 Wiki: Dogmeat (Fallout 3) This is just like in the other Fallout games.

'Fallout 3 isn't the only recent game to feature a canine companion. Fable 2 also featured a dog that would follow the player around and assist him. Both dogs seem to have been designed for similar functions, including helping to alert the player to an enemy presence find hidden items and even assist in battle. The one major difference between the two games is that in Fable 2 the dog cannot die.GamePro: GDC: Fable 2 secret unveiled: smart dog sidekick (March 8, 2007)