Well Tara was quite deliberately fridged in order to trigger Willow's meltdown. The whole of the finale was about the consequences.

Absolutely. But at the very least they knew which emotion they were manipulating. They didn't expect fans to just go "Awww, that's sad."

The ratings [for the next episode] were way down... the showrunner's number of Twitter followers went off a cliff

Awesome. That's the sort of stuff they care about.

And the "We had to kill her off since the actress had been cast in another show" would have been a lot more convincing if they hadn't already written her out at the end of s2, and brought her back for this...