If I'm fighting a major boss in Diablo III (Maghda, Belial, the Big D himself, and so on), is there any way to escape or flee from the arena other than death? Can I quit the game, or yank my ethernet cable?
This can be used from what I read. In a game by your self, pause the game. Then log in on a different computer. This will cause you to be kicked out of the game.
The other thing that I've noticed if you afk too long (about 25+ mins) paused you get kicked from the game, so that could be an option as well.
Both methods could be useful for hardcore mode, in normal mode I would just take the death.
If you are outside of town, the only way to quit the game involves a 10 second countdown timer. Whether you yank your ethernet cable, unplug your computer, or just go to menu -> leave game, the countdown timer will be triggered. Your character will stand still and take no actions for 10 seconds as you wait to leave the game. This occurs whether or not you can visibly witness it.
So, yes, you can leave a game during a boss fight. If the reason you want to leave the boss fight is because you want to avoid death, however, I don't think it's going to work out too well. If you're having trouble surviving while actively fighting back, being completely motionless for 10 seconds isn't going to help matters.
You can do any of the following:
1) Yank the ethernet cable, this terminates communication to and from the server
2) Hard reset your computer (power removal or holding the button)
3) Exit the game (you have to survive about ten seconds or die it doesn't really matter)
4) Log out (same as #3)
There are no ways to get out of the arena, i.e. town portals will not save you. It should be noted it is still possible to have your character die (which is of concern in hardcore mode) and to suffer equipment damage.