Personally, I started hating Brian when Quagmire pointed out all of his flaws and I realized that they were true.
And then, when children were being neglected at Stewie's daycare, but turned a blind eye to it because the woman was attractive.
So, I didn't really care when I saw him die because of that.
(Unlike my brother, who is a HARDCORE Brian-hater.)
Plus, I don't think Seth and the writers have the guts to make it stick for a full season.