[Baalz]

No, the point of the reverse communion is that a bunch of level 1 mages get the benefit of power of the spheres and phoenix/earth/air power (and whatever other self buffs the masters cast). They gain no benefit implicitly from the communion as when they're casting spells they're doing so outside the communion.

So, a 1S 1F slave gets +1 F from the master casting phoenix power, and +1 from another one casting power of the spheres - this bonus (after it is in effect that is) is not tied to the communion. The slave acting on his own is now a level 3 fire mage and can cast falling fires. The master can leave the battlefield, or if he acts after the slaves can still cast spells without mucking things up.