Healers are not magical butterflies
Healers are not hard to find. They are not some mythical creature that must be delicately lured into the guild and then sprinkled with fairy dust every three hours or they'll flitter away. They are in your raid already. They are the kitty druid, the ret pally, the shadow priest, the windwalker monk. In some cases they can even be your hunters, your locks, or your frost DKs.
All it takes is a willingness to try something new.
The same goes for tanks, or for DPS if the day ever comes when support players actually become the majority.
Ask yourself: What's more important to you, playing the role you prefer or saving your entire raid team? It's that simple.
And it's offensive to me that a raid team would simply give up and part ways because no one was willing to switch roles, even temporarily. Maybe the team wasn't that great, or maybe the people in it didn't like each other very much. That's OK. Not every team is a home run. But if you like your team and you want to see it succeed, you can take matters into your own hands.
You're all scared
Now, I'm not saying that anyone can tank or heal well. It takes a certain kind of player to really excel at these roles, and especially to excel and enjoy them.
However, many DPS raiders have never even tried to perform these roles. They don't know whether they would be good at it or whether they would enjoy it.
In my experience, they don't want to do it because they're scared. Yes, I'm calling out all of you DPS out there who have never played a tanking or healing spec. You're scared to step up and play a role that bears more responsibility in the raid and thus receives more scrutiny. You're scared that you'll fail and the raid will blame you and no one will want to bring you to a raid again.
What you're not considering, however, is how grateful your fellow raiders will be when you make the brave choice to try something new. How patient they will be because they know that you've left your comfort zone in order to help the raid succeed. Sure, someone might be a jerk about it, but most won't be. Give your teammates some credit.
If it doesn't work out, then you can go back to DPS. In the meantime, you've bought your guild a few weeks' time to try to recruit someone else for that role. If you don't want to do it after all, no one will think less of you. They'll admire you because you tried.
Officers: Ask them
Many times, officers don't even want to ask people to switch roles. They think it's admitting failure if they can't recruit the right players for all the slots. They think that they'll drive a good DPS out of the guild, or that they won't be able to make up for the loss of a good DPS by recruiting a new, unknown DPS.
Sometimes all people need is someone to say, "This would be a huge help." People like to be needed. People like to be helpful. Yes, even raiders! It may not even occur to them that they could switch until you ask them. So ask.
Flexibility makes you better
Having raid members that can fill two different roles has been incredibly useful since the days of Molten Core, and it remains so today. I could cite a hundred examples, but one of the most recent is the Amber-Shaper Un'sok encounter. Adding a third tank in a 25-man raid makes the fight much easier.
In my eight years of WoW, I've played many roles in raids. I've tanked with two different classes, healed with two different classes, and DPS'ed with four (one ranged, three melee). I can say this with confidence: trying different roles makes you a better raider.
A DPS'er who has played as a healer knows better when to use defensive cooldowns or support spells like Hymn or Tranquility. A DPS'er who has played as a tank knows better how to avoid aggro and how to use misdirect abilities to better effect. A tank who has healed knows better how to help the healers to keep him or her alive. By switching roles, you're not just helping your raid. You're helping yourself, too.
The most successful raid teams aren't made up of individuals individually min-maxing their numbers -- it's a team of players who work together to help each other win by doing everything that's optimal for the team as a whole. Trying different roles provides invaluable experience to help your team optimize.
If you team needs it, I dare you to try a new role. Once you adjust, I bet you'll be better at it than you think.
Officers' Quarters keeps your guild leadership on track to cope with sticky situations such as members turned poachers or the return of an ex-guild leader and looking forward to what guilds need in Mists of Pandaria. Send your own guild-related questions and suggestions to firstname.lastname@example.org.