Hmmm well being new and all...I don't want to ruffle any feathers..but I have read extensively on this subject so here's my take on it.
I read that article..it was in a trash mag...it's from the Star Tabloid, if I find the link I will post it.
Anyways on to my point...Sarah got lots of flack from castmates because apparently they found out that they were out of jobs from an article in EW which interviewed Sarah. Allyson Hannigan in particular made references to finding out this way in a recent article in FHM. As far as I'm concerned...NOT Sarah's responsibility to tell them. It was Joss'. And just because Sarah left the show does NOT mean that the show wouldn't continue. There was much talk about either a spin-off..or a new slayer coming in and taking over. In fact, over this season's eps...they were totally setting up for a new slayer with all of the Potentials, and the return of Faith. So Sarah didn't cause them to be out of work..nor did she do them a disservice by not running to them and telling them. For all we know..Joss could have said to her "look I'm not sure about the future of the show without you..can we keep this quiet until I decide."
As for the wrap party...Sarah was in Vancouver filming Scooby Doo Too..which has her pretty tied up. AND, they had a farewell luncheon for all castmembers and crew...at which time Sarah gave them all leather bound books of some sort. (Everyone, even crew members).
I have heard so many nice things about her..people who have met her and have shown me pics of them with her..that I just don't believe anything an unidentified "INSIDER" says ...notice how nobody is named? It's always an "insider" or "source." Names already!!!
I lived in Vancouver for 2 years when I was a teenager, and I saw how many hours movie sets would have streets etc. blocked off for filming. Sometimes it's just impossible to get away from a busy schedule like that.
I'm not saying that it wasn't rude to not show...but maybe between the various crew members and Sarah's busy schedule, they couldn't get a time where they could all be available..and if more people were available on a certain date, then they would have to go with that date. I think it's nice that they didn't just work around what people have dubbed the "star" of the show. This shows that each and every castmember contributed to the show's success.
In closing..I'm sure if Sarah had wanted to, she could have said "sorry that day doesn't work for me, do it THIS day" (which might not have been good for a lot of the other castmembers. But she didn't.
Sorry this is so long, but it's just my take on it!