Maybe it has been too long since I played through Oblivion, or maybe I'm missing some of the lore, BUT....
I was recently thinking about this:
The Dragonfires - in the Temple of The One - are supposedly what keeps the gates of oblivion sealed.
Allegedly, as soon as an Emperor dies (ie Uriel VII), the Dragonfires die out, THUS leaving an opening for Oblvion's assualt unless they are re-lit by the next Emperor.
My first point is this:
Seeing as Martin Septim essentially died shortly after re-lighting the dragonfires (and turning into Akathosh's aspect), wouldn't the dragonfires immediately die out again?
I can't remember any reason given for why they would remain lit, HOWEVER - this also provides one of the only explanations I can think of as to how they could remain lit during the 'Mede' Dynasty.
It is referenced that only those with the 'Dragon Blood' (and thus in possession of the Amulet of Kings) could light the dragonfires.
As of Martin Septim's death - Talos' line of dragonborn emperors was officially ended. (It is also assumed that the Amulet of Kings disappeared along with Martin Septim).
How do the dragonfires remain lit - or are they even at all? To me it was generally implied that if the Septim line was destroyed (removing the only line with the dragon blood), the dragonfires would remain un-lit - allowing for all-you-can-invade Daedric chaos.
Again, I'm sorry if I just MASSIVELY missed or misinterpreted anything regarding this aspect of the lore, but it occurred to me recently and I realized that I did not have the answer.
Enlightenment on this matter would be much appreciated. Other than that, also feel free to speculate with me.