The PCs did it, but it was future versions of them who time travelled to the past to start it. They have to figure out why they did it in the first place, before paradox unravels the time-stream.

If you can turn a sea to blood, then surely you can make it Holy.

Of course it would require a great deal of Faith...

sure but how much time? you could say you only start healing a day after the injury and that'd fit the text just as well.

I don't see any problem doing this, since high Conviction/etc give you extra Minor Consequences instead of stress boxes, and all you need is an excuse to start healing - hit the hospital or have a bud around to do first aid after doing your bloody ritual and you're all back to normal. What's the big deal, having Supernatural Recovery? You can use your single moderate consequence? pfft. Being able to heal some of your consequences during a turn? pretty nifty - but not more nifty than just having more consequences via a Stunt. Being able to heal without an excuse? It's okay but not game breaking.

I've seen plenty of movies or whatever where the BBEG powers a dark ritual by chopping off his hand or opening up his arm only to have it heal a moment later. Psychic or Social trama would be awesome too. All the consequence is, is justification for another maneuver.

Also, EMP hardening often happens by just using older technology, which is more resistant to EMPs (like say, vacuum tubes). Still, not too much better - Harry still likes to burn out lightbulbs, apparently.

Depends what you mean by EMP hardening. How do you think people go about EMP hardening?

time magic to prevent them ever becoming a black court in the first place.

Use a paradox-performing ritual to keep their personality/memory the same at your option.

Possibly just drag them forward in time instead of seeing 'who would they be now if they were never a blampire'

I'm actually willing to say that True Blood vamps are weaker than Dresden Files vamps. Obviously there's quite a bit of power difference between Jessica, Bill, Eric and Godric, but when all's said and done their powers are more plot device than straight up strength. I would let them spend Fate Points to do invoke some impressive feats on their Aspects but they are merely inhuman (It counts as Ritual Magic: I Am Vampire at most), with elder vamps having higher skill caps.