IMO that black-red thing in the end of trailer, was a spell that enchances sun to make it's light harmless for vampires instead of disabling it.
Is this a serious post? (asking honestly, no offence intended)
If so, I don't think so. In my opinion it's an epic spell brought on by an Elder Scroll that simply blocks the sun, maybe an eclipse of some sort.
In response to the OP, good theory I guess. Possible answers...
- They're not that smart and haven't really thought of the consequences.
- They know the consequences but don't care.
- It's a fantasical world, not all animals breathe oxygen, not all plants require sunlight.
- It's for a limited time only.