Bear in mind that if you abandon a duty you get a debuff which means you can't queue for another one for half an hour, but that doesn't apply if you get kicked. Besides, it's hard for a healer to be so irredeemably terrible that the group would rather kick them and re-queue than carry on, and a tank/healer leaving usually means the whole group disbands because nobody wants to wait around for an in-progress group, so I'd always be inclined to try and tough it out unless it's apparent that you're just not going to get through the place. And if that's the case you can vote to abandon instead, in which case the whole party disbands and nobody gets a penalty for re-queueing.