Well, I will begin with a good fact, namely, that in the episode "Spell with no name", the rooms that were shown "cover" not only the past and present members of the royal family, but also (judging by the dark corridors, where the "shootout" between the Narwhal and the Untitled happened, and the existing doors with previously unknown symbols) stretch a long way forward to the future owners of the wand. This, obviously, means that after the destruction of the source of magic, the wand will continue to exist ... or will pass into a entirely different form. And this also leads me to think about the degree of dependence of the "room" and the spells themselves from the minds of their creators (past, present and future).
Spells of long gone queens and kings(let's not forget about Justin) continue to exist inside the wand and, in addition, each new member of the royal family also creates their own spells, which may differ from previous ones. (The most striking difference in physical forms is seen in the example of Eclipsa’s and Star’s spells.) So I'm wondering where do spells come from and at what age (of owner of the room) do they begin to form? Is there some kind of "energy and matter reserve" for future spells in each room? Do spells take shape and mind when the wand falls into the hands of a new owner, or only when she or he first uses magic (in any form)? And, the most burning question (at least for me) is, what happens to spells in the room of the half-monster that has been brainwashed for almost 300 years in a row?
If we take into account Olga's memories, Heinouse’s magic in began to show itself very early, and it is quite possible that the spell (of one particular "soul-eating" kind) could have been used at a very early age... and maybe Heinous even secretly tried to learn how to use magic. Anyway, the “magical push” could have been given, “energy” could have been used and one spell could have been formed... and then the brainwashing started. With all that, if we remember the dependence of the "room" on the mind, it is terrible to imagine how hard HER room and everything in it began to " twist and turn".
There may be many point of views on this matter, but there are too many different horrors and games (like Alice American McGee, Evil Within, Layers of Fear and etc.) in my head, so I have one quite specific idea about the possible "structure" of such dimension. It is a dark, constantly rearranging place, with a lot of hidden passages, destroyed and twisted rooms, endless corridors and a lot of shapeless spells inside... A really “quiet” place, where, for a long time, after each wash, only one and not the most “good” spell took it’s shape again.
However, at the same rate, all this could have become the cause of Heinouse’s/Meteora’s great strength in magic. I still hope that Meteora’s and monsters’ magic doesn’t depend on one "radiant source" (with crystals and unicorns), but is more... "balanced" kind of thing. (as a fan of "Alchemy's Law of Equivalent Exchange", I am a little confused by spells that can give anything but take nothing in return). If all Meteora's magic can come from the energy of souls accumulated before her rebirth, then the variant with the possible future preservation of all magic and its transition to another form doesn't seem so impossible.
Of course, if Star really destroys all magic, then her "good deed" can turn out to be something incredibly horrible - in addition to the problems that will represent the lack of magic for the main characters, it is difficult to imagine the scale of the "Apocalypse" (caused by the "effect of one Butterfly"), that will envelope all those races and living creatures, whose lives depend on magic. In other words, we are yet again left with a lot of questions... but also with a little hope that everything will end well.