[Dave]

I think part of JKR's idea was to keep you guessing whether Harry would die or not (I predicted wrongly that he would die, though her explanation of why he survived the removal of the Horcrux was a little weak, I thought.) Or if not Harry, then a major character as has already been mentioned - McGonagall, Hermione or Ron. With so many dying, you would feel it possible to lose any of them, though it did begin to feel like the final episode of 'Blake's 7' or the end of 'Serenity'.

I think the 55 dead mentioned would only be adults, or students who were 'of age' (unless they sneaked in like Ginny.) The younger students were all evacuated first through the corridor to Hogsmeade long before the battle.