Well, as I have done that run a few times as holy pally here is my input. None of this should be ground breaking, but just ensure that it stays in the front of your mind as that portion of the fight does get intense.
Do your best to keep eeryone completely topped off before that portion. if they need to bandaid on their own, then make sure they are aware of this.
If you have a lock, ensure everyone has a fresh lock pot. Super healing pots are also cheaper than a wipe. Make sure they know this.
If everyone(not you) pops a healing potion, it will be a much cheaper investment that multiple wipes.
Also, You have to fly away from those energy things, and it will significantly lower the damage. It will still be about 1k a tick, but not huge insane amounts.
Here is what I do personally when that part happens. I immediatelly pop divine illumination. I am going to be casting something like 1-2 fols to top the first two people off, and then go into straight holy light mode for the next 10-15 seconds, so it is vital i am saving myself the mana. Also, on whoever is last(or came with low stamina), make sure you have saved your divine favor crit for this time.
Also, pop the Prayerbook trinket. If you are a draenie, then you may start that portion with a gift of naruu on the tank.
If you are not having problems with mana, but having problems keeping that last guy alve, do not forget about holy shock. It basically is a fol that lands 1.5 seconds sooner.
And lastly, if you are low on mana but have not used a potion, pop lay on hands on the lowest guy, who ideally will be your tank, and then pop your mana potion to bring your mana to a reasonable amount.
And it is interesting that you bring up maiden because this fight reminds me of maiden. It is a very healer intensive fight. You really need to be on your game. That fight is ultimately up ot you. Obviously the higher the dps, the quicker the fight goes, but it will remain intense through the entire duration.
I have only been in Mgt 3 times, and have not yet wiped on that portion, but only because I was warned that this fight was basically my baby.
Unless you have reason to believe your tank is complete crap or your dps is week, if a wipe happens their the onus is ultimately on you, assuming the dps popped pots.