As much as I'd like to think I'm an extremely dedicated and reliable guild member and as much as I live and breathe tanking in the end-game content, even I am forced to admit that I sometimes do that thing raid leaders dread most. I flake out. It's not like I'm lounging around my man cave, sipping an incredibly powerful beverage, and just spontaneously decide "I'm not going to raid tonight. Screw those 24 (or 9) other people." It's always a real life thing for me: I run late at work, I'm getting married, my cat's on fire. (I've missed three raids because my cats have caught themselves on fire. Once is funny, twice is a concern, but I don't think anyone believed me the third time.)
But no matter how real and valid my reason for missing a raid, the fact still remains that I'm letting down a group of people. (Or, I'm letting down a group of friends if that's the flavor guild you're running.) Even worse, let's say I'm the main tank. Many raiding guilds use a deference-minded loot system: "main" specs get the loot for their role first, before people who only fill that role on occasion.
So, not only is the raid missing a warm body, they're missing a warm body who is usually the most practiced at their role and the best geared for that role. It's a conundrum for every raid leader. You don't want to tell your Class A folks that if they miss a single raid, they'll find themselves benched. But at the same time, you're really out a whole lot of power by missing those folks.
This problem is especially palpable for tanks and healers. That's not because DPS isn't important (it absolutely is), but because the tank and healer corp for raids tend to be much smaller. If you're missing one healer out of your 10 man raid, you're suddenly down 33% of your healing power. (Best case scenario might be you're putting the two-healer stress on someone, but that's still not great.)
The only way you can mitigate your raid loss due to missing tanks and healers is to plan ahead. Let's take a look behind the cut and talk about how you can handle this issue.