Urg she totally does. Whatever happens to gale all we know is that he has some job in district 2. :( as to prim dying I really have no idea why it couldn't be someone else.
Katniss doesn't annoy me but the whole Gale thing does. He just vanishes off to district 2 and Katniss never sees him again? That doesn't seem right to me.
Prim died so that Katniss would kill President Coin. If Prim didn't die, Katniss wouldn't care what happened and The Hunger Games would just keep going.