Yes a definitive answer from the mouth of the oracle itself would be good. Hoping it won't be 'cull them'
I too have some sheep with shredded ears, but they're older and not going anywhere so their replacement tags live in the house with their pedigrees. Tags inevitably have their drawbacks, but so do boli (which are easily coughed up) and pastern bands (which could constrict a growing leg).
I'm sorry to hear that your sheep were attacked by a dog. A slight comfort is that the dog may have swallowed the existing tags and will have some problems ejecting them from the other end. One way to identify the culprit - scan it !
Please let us know what Defra decide.