As they are saying it's important to stay in the fight, even if you become "main healer" as the dedicated healer goes down. Stay within Melee range of your target and continue Judging and Exorcising as the proc goes off, and throw in your Crusader Strike. This will net you Holy Power and Mana from JotB while keeping your damage relevant.
The way Ret works boils down to the fact that it generally uses very little mana but burns HoPo for damage, so when healing you'll generally want to use excess mana for heals and also make sure to help out with Cleanses. This means Flash of Light is almost always your best bet. Only in true emergencies should you use HoPo to heal yourself or another player (with Word of Glory), as it will detract from your DPS output. When an Emergency does arise, ask yourself what you can do BESIDES healing first ->
1. Can one of your Hands help the situation?
2. Could grabbing threat on 1 monster off a group in order to take pressure off the tank or to grab threat off a non-plate ally be a good choice?
3. Is it possible to Repent? Stun?
If severe healing is absolutely needed, continue to stay in melee range of the target and continue your HoPo gain to use for WoGs. Continue Judging to keep you and your party's Mana flowing. Use Flash Heals and WoGs.
Warning - Attempting to patch together any coherent message from my posts may result in chronic headaches and/or intense vomiting.