It won't end until after the Welfare Reform Bill becomes law, although if the government gets it's way, it will take effect from April and apply retrospectively to include the initial 13 weeks of the claim. Bear in mind that with a claim that goes on for a long time, a claimant may spend some time in the support group and some time in the WRAG, but it will not be which group you are in when the new provision comes into force that will determine when ESC(CB) ends, but how many days you have spent on ESA other than in the support group.
This is supposing that the Bill isn't amended.