...it could be easily argued that the main energizer wasn't providing power but merely re-charging the dilithium crystals.
...Well, not exactly. The device in "Alternative Factor" wasn't called the main
energizer specifically. Perhaps the TMP version of the ship has several, and the one called "main" is the one that nurses the crystals back to health in situ
, without the services of Lt Masterson and her special department? Thus, when Scotty says the "main energizer" or "main energizers" is/are out, he's saying that main power is out because the crystals are screwed (a somewhat standard occurrence, perhaps) and stays out because the energizer cannot "unscrew" the crystals in situ
(an unusual situation). That's why he had to "take" "the mains" (the primary power system) offline - because most of it is working, but a single component is not, and the means of repairing that single component is damaged as well. Spock knows he can bypass the repairing device and repair the component himself, after which Scotty could flip the switch back on.
We just know from Spock's actions in that room that he was able to bring the main energizer back online
Again, not exactly. After Spock is done, "the mains" are back online, not "the main energizer" explicitly. And I postulate the two are not the same thing; the former is what one calls the entire main power system, and the latter is a component that serves this system.
So it looks like the radiation in the room can be decontaminated in 2 hours but only after the warp engine was taken offline.
I'd argue the room is off limits for two hours if nobody has unscrewed the cap to the radiation-filled dilithium crystal dumbwaiter
. If somebody does that, the room is off limits for two years
As to the radiation lifeform on Genesis, IIRC, it was from the super grown worms that were clinging to the photon casing. Spock was the detected "second lifeform" and I don't think they mentioned any radiation coming from him.
We could argue the corpse was initially radiating, and contaminated the insides of the coffin as well. When the reborn Spock left (and his method of doing so is a bit mysterious!), the coffin stayed contaminated, and that's what the sensors observed. But Genesis somehow removed the radiation contamination from Spock's rejuvenated body. Hell, it ditched a lot of body mass somehow, so why not the bad parts? Perhaps the bad parts became those worms?
The room might eventually have been decontaminated by machinery available at a starbase. But I'd wager it was never decontaminated, and burned up in the Genesis atmosphere in a still contaminated condition.