I don't think the actual knowledge of Buffy being in Heaven would have changed much, in fact, we see in the show that when they do find out, it changes absolutely nothing. They continue to heap more and more troubles and responsibilities on her shoulders, and I don't feel they ever made any effort to aid Buffy through her depression. Even when they did talk about what they did, they did so without Buffy. In trying to find how they all felt about taking Buffy from Heaven, they failed to speak to Buffy about how she felt about being taken from Heaven. This was clearly not a group of people capable of handling a friend's emotional and existential crisis, let alone a full blown depressive episode.
For me, it wasn't the fact that she had been pulled from Heaven that Buffy needed to express to the people around her, it was that she was struggling, pretty much every second, to just exist. How she was feeling is what needed to be known, not where she had come from.
Given the nature of Willow, Tara and Xander's story lines I don't know if any of them could have helped Buffy, or even themselves. But Giles. Giles should have been there. In fact, he was duty bound to be there for Buffy. He was also wise enough to know that what Buffy was facing was not just a "bad patch" or a shirking of her responsibilities; she was ill and she needed looking after. She needed her watcher.