One thing that always struck me as strange in the premise of Wrath of the Immortals is the notion that use of the Radiance would mean an inevitable drain of the Prime plane's magic. That's definitely not true, and Immortals should know it! The spell Trascend Life Force (from GAZ 3) that allows an experienced Radiance user to become an Immortal, can fail; in particular, it can fail because the caster fails to complete the last ordeal, the duel, in which case the caster's lifeforce is imprisoned in the Nucleus preventing any drain of magic from occurring for 1 year/caster level. Basically, all that the Immortals of Energy have to ensure is that every century 3-4 high-level mages discover and cast Trascend Life Force, and fail at the very last step. The only problem I see is the Star Dragon complaining about his teeth (one tooth per casting is needed)!
And, indeed, this sacrifice practice seems to have been the case throughout the centuries. In AC1000, 50 rad force has already been drained from the prime. This corresponds to no more than 50 years of Radiance use without a life force to fuel the Nucleus -- possibly less, since any year with 6 or more radiance users (as in the case of AC1000) drains 2 or more rad force if the Nucleus lacks a life force to power it. But we know that the Radiance has been discovered as early as 395AC (from the Glantri timeline in GAZ3), i.e. 605 years before AC1000, so almost all the time since then it must have been fueled by imprisoned life force. This is particularly true after the first few years, in which the first discoverer(s) were still struggling to understand its powers and none had yet managed to cast Trascend Life Force.
Then why all the fuss? Well. Perhaps, Rad in his haste has lost a few rads now and then, i.e. has allowed the Nucleus to very occasionally run unfueled by a life force. Nothing has come of it yet, but Ixion worries about the danger (every rad drained is one more step towards annihilation of Energy from the Prime) or perhaps by just more subtle effects that have no in-game mechanical effects but are there nonetheless.