Lets look at it logically from what I perceive is the reason why management decided to have no 13th month for Captains. Its all to try and push A and B scale captains out of the company if the can.
Firstly, it takes 10 years plus for Command. The ones on A scale and B scale are will into their 40's - 60's. So the chances of them moving to another company due seniority is not that high so they are kind of stuck between a rock and hard place.
In saying that the ones that do pick up and leave to go somewhere else, is only a benefit to the company in regards to monetary compensation compared to a C scale. The only "talent" the company will want to hold onto are the ones that can do check and training, and Dragonair can help in this department if need be.
Lets say X amount of Captain leaves, they need to be replaced, therefore time to command is reduced significantly, which will tempt new DEFO's, as I'm yet to hear "Oh 10-12 years to command! Where do I sign?" Most will walk out of the interview knowing other Asian and ME carriers are doing it in about 4 years.
Going back to Dragonair, I believe CX is going to absorb them into their AOC and therefore leaving a spare AOC. With 20+ new A320's ordered this might be for Cathay to launch a new low cost carrier.