I was thinking about Magnus fleeing to Aetherius and it got my mind racing.

I have a few questions that I'd like any answers to or speculation on.

One: Theoretically, could Magnus and The Magna Ge come back through the holes to Aetherius they created ? And if they could, would they be just as powerful as they were before the mortal plane was created/ probably still are due to them fleeing, or would they be somehow bound to Nirn like the Aedra and there power to escape it lost ?

Two: The Magna Ge are described as other Anuic spirits that fled creation. Did the other Anuic spirits that stayed behind become the Ehlnofey ?

Three: Am I then correct in inferring that Padomaic spirits that followed the various Daedra princess to the various planes of Oblivion became the various Realms equivalents of Ehlnofey, which In parallel to Nirn Devolved into various forms of Dremora and lesser Daedra ?

Four: I understand that the Mantellan Crux was used to protect the heart of the Numidium, what I don't understand is why in Aetherius, Deadra and Undead are the ones protecting it ? Is it simply because a Mage from Nirn bound those beings to it ? Why would Mangus/the Magna Ge tolerate these beings there ? Or would they have been locked out of it magically(Unlikely considering Magnus would be the source of the very Magika used to do it)? Or would they simply be indifferent to it as it concerns events in mundus ?

Any feedback/ theories or comments would be appreciated, cheers.

1. Probably yes but most of them have no reason to do so. One has already returned in the form of a Daedric prince, Meridia.
2. The Anu/Padomay division between the aedra and the daedra is aldmer propaganda. Disregard it. All et'Ada are mixes of Anu and Padomay. As for your question, yes, the more powerful spirits became the earth-bones or the laws of nature, the divines and the rest became the Elhofney and eventually devolved into the separate races.
3. The form of a daedra is directly linked to its level of consciousness and power. They can theoretically take any form they want but its easier to take a common form, possibly designed by a prince than to come up with your own. The weaker daedra take simple, weak forms such as clanfears or scamps, scamps being sort of a universal low-level daedra that all princes support. The more powerful ones take other forms such as xivilai, dremora or aureals etc.
4. There isn't anything preventing the daedra from moving between oblivion and aetherius as they aren't bound in the way the aedra are. Magnus would probably have to begrudgingly agree that the princes were right in not following Lorkhan. Magnus and the Magna-Ge have nothing against the Daedra, heck there is probably a lot of spirits in Aetherius that never participated in the creation of Mundus or chose to create realms in oblivion.

4) Or that Daggerfall wasn't really complete in its lore (wasn't until Redguard that things went the way they are), so the trip to the Aetherius could be viewed as semi-incomplete.

Personally, I'd say the Agent did make a trip there, found that Mantellan Crux (which was supposed to be a substitute of Lorkhan's heart, not protect the heart of the Numidium) , and waved at Sheogorath.