As I understand it CC have historically had a habit of going sick rather than on strike, which is why it was well publicised in advance that being sick would be regarded as being on strike - unless one had a doctor's certificate to back it up.
Anyone who didn't get a doctor's certificate has no one else to blame, but if they did have one and are still waiting for their money they should get their rightful pay in the end without legal recourse.
The comments about 1000+ still waiting does not make it clear whether they are certificated or not. I find it difficult to believe that more than 1000 people went sick without getting a doctor's certificate, given the advance warnings, but also BA would be very inefficient if they have still not paid people who supplied a certificate.