I first heard Brian was dead because someone posted one of those pics about it on my Facebook newsfeed, a quick run to wikipedia filled in most of the blanks for me, all I haven't seen is the episode itself yet.
Truth be told, I'm not that sad that they killed off Brian. I wish I could say that I was, but I'm not. Actually it makes me really applaud Family Guy for taking a chance and really killing off a main character like that.
In earlier seasons, Brian was one of my all time favorite characters, the witty alcoholic "uncle" character who was more libertarian or just not all that political at all in his initial run ("This is why I don't vote." ~ Brian Griffin) than the left wing, anti-religion radical he later became (basically a less interesting Hailey Smith if she were a dog) due to him basically being a writer's surrogate character, and the only times I found myself caring about him in any story were the fun team-ups he had with Stewie such as Stewie and Brian join the military, Stewie and Brian build a house together, etc. etc.
What DOES bother me though from what I've read though is HOW Brian died...hit by a car? That's it? That just seemed like the writer's spent a whole day trying to come up with something and then at around 11pm once they finished the Chinese Take Out they just kinda went "Okay, fine."
The show started in 1999, it's 2013, that makes Brian (arguably) 14 years old. They could have done an incredibly meta story about him dying of old age, or even (not to invite even more Simpsons comparisons) make him die due to the faults or actions of an existing character.
I dunno, being hit by a car just seems like a weird way for them to go about it.
Will they bring Brian back? I dunno. A small part of me is actually hoping they don't, but with the amount of fan backlash over this it almost feels like they would have to.