Mystra banned all spells above level 9 on Faerun. That's one. And even that only applied to FUTURE mages, so any lich, immortal etc. that had those powers still retained them. So even in present day Toril it is absolutely possible to encounter someone capable of casting level 10 and 11 spells.
This is absolutely false. Neither Larloch nor Ioulaum or any other Netheril survivor could cast any of the 10th and 11th level spells they knew back then. It would be completely idiotic to restrict future spellcasters and not those from the society actually responsible for Mystryl's death and the collapse of magic.
Epic spells, with their Seeds and spellcraft checks are different from 10th level spells, and a mistake imho. It is good that most sourcebooks ignore their existence entirely.
As I've mentioned before, Planescape makes it abundantly clear that, no matter how "dead" they may appear to be, a god can always return. Always. Even fucking Aoskar's return was a possibility, and he was quite literally consumed by the Lady of Pain.
It is possible, yes. But it is exceedingly unlikely. And it should never, ever be done in a footnote between editions that erases all our efforts as players to prevent such an outcome. Or as a prelude to an adventure that kills off a beloved character and retcons away most of his achievements.
