If its any help, I had a ewe with the sort of mastitis that causes multiple holes in the udder. The vet said it can spread to other sheep unlike normal mastitis, so best to keep separate and good hygiene.
However, Just to give you hope, the sheep fully recovered, and altho I didn't put her back in lamb and later sent her off for the chop, she did make a complete recovery. Best to check with vet whether yours should be used fr breeding again, mine seemed to think there was a risk of the problem recurring with this specific multiple cyst type, so I didn't risk it.