How does wiping out Sunnydale...

[Mulderzmandy]

Kill the First?

Yes--his army is defeated, but that was just a bunch of vampires.
He's pure evil, so I don't see why that losing his army would kill him. He cannot be dead--Why can't he just go haunt them in Europe?
Or torment someone else? I mean, not to pick on the show, but he can be anywhere as anyone--so he isn't gone, right?

 

[phoenixrising]

The First isn't killed, but its plans are seriously disrupted.

Look at it this way; the First is the essence of evil. It has no corporeal form; in fact the first time it appears, it has to be summoned by the Bringers. Somehow, the death and resurrection of Buffy makes it easier for the First to manifest itself and enter certain people (Caleb for instance). The First is tired of waiting and sending its minions to take out the Slayer, so decides to do the job itself. By killing all the Potentials, it will be able to enter anyone. By defeating the Turok-Hans and sealing off the Hellmouth, Buffy and the others disrupts the First plans, making it have to start all over, but this time with hundreds, possibly thousands, of Slayers now active to oppose it.

Basically, most of season seven is the First starting to cast the spell (for want of a better analogy) to become solid. Buffy and Co. screw it up, causing it to have to start all over again.

So, the First isn't dead (how do you kill the essence of evil?) but thrown back to square one.

 

[Helpless]

Well, I guess you could put it that way but if you do...the show is never ending, the evil never stops and it would be on-going until the point of viewers losing total interest. It had to end somewhere and that was the perfect way. The Firsts plan was defeated and yes, it can go haunt or stir up a plan somewhere else but that is rather fast and it is highly unlikely.

It's a tough one to state but I'm just gonna leave it at that the show had to end...