Whenever someone does that in a group i'm in, i recall immediately, and they do end up soloing. A few nights ago, a friend of mine had an lfm up that stated "team oriented players". We end up in ghosts of perdition? Whatever the beholder quest in necro 4 is. Some guy on a wiz enters the quest and takes off, before everyone has even arrived at the quest entrance. Gets the dungeon alert up to orange, leaving basically everyone behind him to eat his sh*t storm. I personally got mobbed by a host of wraiths, including a red name, and had no chance. So i said sorry i really hate zerging and recalled. Heard later that everyone ended up wiping, and the 'team oriented' guy who made the problem ended up dropping without a word.
So who's fault was this? I guess to you, it was ours, because we don't play that way.