Sonja says: "Well at that point it won't be my problem anymore, will it?"

Oh and the information about Akatosh and St. Alessia is right in that book about The Dragonborn you find in the jail on your way out of Helgen, and again in Sky Haven Temple. It is pretty symbolic and vague and you can't take it literally as some magically bestowed gift of dragon blood. Someone in the bloodline, namely St. Alessia..... well you know.
Akatosh did manifest at the end of the Oblivion Crisis to defeat Mehrunes Dagon using Martin Septim as his vessel. Dead? I think not.
Not dead as a mortal is dead, but dead as a god is dead. Its not the same thing.
Lorkhan is arguably deader than Akatosh since he got his heart torn out, but many shezzarines have walked Tamriel.
Even dead gods can dream.
Aedra do not manifest themselves directly on the Mundus. They send dreams, visions, avatars.
Part of the reason is that they
are the Mundus.
The avatar of Akatosh that appeared was summoned by Martin, it required his sacrifice. It was the fulfillment of the Alessian pact.
In a way Akatosh did not even exist before the middle dawn, so it is also a nice symmetry, a fullfillment of purpose.
"Akatosh, looking with pity upon the plight of men, drew precious blood from his own heart, and blessed St. Alessia with this blood of Dragons, and made a Covenant that so long as Alessia's generations were true to the dragon blood, Akatosh would endeavor to seal tight the Gates of Oblivion, and to deny the armies of daedra and undead to their enemies, the Daedra-loving Ayleids."
This is of course wonderful Imperial propaganda as you can view it this way, however it conveniently leaves out the reshaping of Auri-El by the Marukhati Selectives, namely to create a god worthy of leading the Imperial pantheon.
Akatosh was bound to the empire and compelled to the covenant as much as Alessia.
I would say it is unlikely that Akatosh engaged in a physical relationship with a subgradient as Alessia.
Its almost an incistuous concept.
I cant think of any other comparable Aedric-mortal relationship in the mythos.
It is however, a fascinating idea.