I have the same problem. My honey Braggot bottles are all flat. I know what I did wrong.
I forgot to cool my racking sugar down to room temperature. I pitched 200° racking sugar in my priming carboy and most likely killed all the yeast in my wort.
Can I revive each bottle somehow?
I don't know how many millions of threads we say this in, but pitching boiling sugar into your bucket WILL NOT KILL ALL THE YEAST.
2 cups of boiling liquid is in a head to head collision with 5 gallons of not boiling beer... realistically, who do you think is going to win the battle? By the time 1/2 gallon of beer dillutes the sugar water it's not going to be boiling anymore is it?
Even if you killed a t-spoon of yeast in that first little bit of beer that hits the boiling sugar, do you really believe that the billions of cells in the entire rest of the beer is going to die as well?
I know when something goes wrong we're always looking for 'what ifs' but we can't throw basic logic out the window.
Your braggot didn't carb because it's 12% and that's a really high alcoholic environment for MOST yeasts to thrive in, let alone the tired yeast you used to ferment the beer with.. and even most yeast you could have added at bottling, may not thrive in the environment.
You'd need to use something like a champagne yeast to carb it.
Besides, according to Wyyeast's definition of Braggot, it's not very carbed if it is at all.
"Carbonation will vary as described in the standard description. A still braggot will usually have some level of carbonation (like a cask bitter) since a completely flat beer is unappetizing. However, just as an aged barleywine may be still, some braggots can be totally still. Overall Impression: A harmonious blend of mead and beer, with the distinctive characteristics of both. A wide range of results are possible, depending on the base style of beer, variety of honey and overall sweetness and strength. Beer flavors tend to somewhat mask typical honey flavors found in other meads. "
You could try a slurry of yeast, with an eyedropper and fresh caps, but then you'll still be waiting.
Me, if the braggot tastes good as is I wouldn't mess with it.