We've had our first couple weeks of this in game, and already I've heard "Be right back, Tornado," from some guildies living down in Kansas. Luckily everything was okay and no one got hurt, but the fact still remains – we lost our head Mage for 30 minutes, and that's 30 minutes of our life we can't have back!
While a Mage having to take a break in the middle of raids isn't a show stopper, having the main tank (my role) go offline is. I've had the unfortunate situation of having that occur a couple days ago. The computer I was raiding on wasn't plugged into my UPS (Uninterruptable Power Supply), so I was disconnected from everything when we lost power for about 30 seconds. However with a bit of tinkering around, I was able to put myself in a situation that lets me stay on even when the power hiccups.