I used that scenario because in this instance 3 of the 4 knew one another. They probably know one another's main and secondary jobs, and know what pieces each other needs without really discussing it. The healer really is the odd man out going into an unknown situation. I agree, that the healer can ask as well but it would have also been polite for one of the three friends to speak up.
I do many runs where it's 3/4 of us are FC members and we usually always tell the 4th person, 'We are all from the same FC and friends, so speak up if ya have any questions or need something~!'
But once again that is assuming that the healer was in a position to do that. We don't know what time the run was, it could have been early morning and no one was really on so the healer had to run solo. Or maybe they were getting ready for work and were just doing a run real fast before leaving. It could be they don't have an FC, I see many people in Mor Dhona decked out without an FC, because it's not everyone's thing. I even had a friend where he came back and the FC had decided (granted it was a small FC) to call it quits and he no longer had an FC. There are so many 'but what if it's this situation' that there is no way that anyone in a DF can know.
Which is why, as you agreed:
A simple "If someone needs something in this dungeon or needs help, speak up!" would fix a lot of issues. If people are too lazy to type it, macro it. We could sit here going back and for all day about what if's, but it's all assumptions. Just cut the assumptions out and take 5 seconds to be polite and bam, no more assumptions. If people don't speak up about needing something that's their issue, but at least it was asked. :)
