Idk what SE is thinking with these char limits.

Edit:
The Cleric button is bad. Odds are when the healer dies you're finishing your cast, pressing Cleric to turn it off and then STARING at your buffs to make certain it's off (I.e. it accepted your button press and you didn't accidentally click twice). You also need to move into position—BLMs are jerks and like to stand at the furthest edge of the arena, and if there's multiple BLMs they'll likely be at opposite ends just to F@%# with you. So you eyeball it and try to position yourself between BLMs and the tank and then begin casting your AoE heals and what have you.

So that's the standard process which is slightly more annoying than provoke + shield lob/tomahawk/unmend. There are things you can do to help, for example casting instant heals while you move into position on those needing them urgently, or using something like LighttSpeed to heal as you move to position. It's not that hard to pick up after a dead co-healer, however there is a brief panicked moment where you need to do things right or the rest of the fight goes downhill.