Of course it's dying down. Who hasn't expected it to? But I don't like the expression ' it's already dead and buried '. That's a typical media exaggeration.
I mean if you think about it, it's more than obvious that user numbers are decreasing. This isn't the first time something like this happened and it's always the same pattern.
1. The Hype: FaceBook got really popular over the years and actually became the #1 social media service. It attracted lots and lots of people, because it was good and new, but even more people got sucked into it by peer pressure.
2. The Peak: Once the hype has reached its maximum it'll stay like that for a while. But this is as big as it gets.
3. The Drop: People start realizing there's alternatives to it and that it isn't as good as they thought it was in the first place. Numbers start decreasing quite rapidly.
4. The balance: Even though numbers may be dropping, FB won't die, but it obviously couldn't stay at its peak either. Once everyone who just registered to be part of the hype is gone and only people who use FB because they like it are left, you'll have your balance.
I'm not saying it will never die, it may actually. But IMO, if that is ever going to happen, it'll be in the far future.