Just starting to run Heroics and have only had the pleasure of a couple non guild runs and let me tell you that people just need to relax a little bit.
Running a random yesterday with a friend, we had someone leave the group after a wipe because the healer did not run back. Not that the presence of the healer would have made any difference by the time they got to us mind you.
After that, a mage replaced that person and the group went on without any issues. Even when we wiped on a bad pull that could or could not be blamed on a certain hunter. The jury is still out on that one. But everyone else just laughed that one off and finished the dungeon with no other issues.
So just take a deep breath everyone.