So if I'm assuming correctly Mr. Priest became unworthy of the power of the angels, but instead gained favor with the Sins and as such can manifest their powers or even summon them.
The condition to summon them would probably be a surplus of emotion with the associated Sin, which is why Mammon...
I assume the latter as Fiona was the one to start this loop with the party in their strongest iteration. I presume even if Rayman can start a new loop there is no guarantee Albus and co will retain their memories this time around as Rayman is the hero now.
I mean in a way Raoul is keeping tabs on the demons as he was wondering about Theodora's condition and went out of his way to give her a letter, so I would assume he will play a role in the Demon Queen's downfall.