Maybe LGC are going eventually - maybe not. That is the problem with policy uncertainty...
Whatever the mechanism will be derived to support renewables, it will be it is likely to be applicable to all renewable energy sources. That will include old and new clean power sources.
LGC are reducing in price recently however: http://www.demandmanager.com.au/certificate-prices/
Given the Lake Bonney asset ages I am guessing they have provided significant value already and have amortized a major part of their cost. If I had the time I would find the numbers - anyone want to do the research and maths?
Lake Bonney assets were quoted at ~0.87 loss efficiency factor on the 2017 report. I suspect that the battery will improve that output value and offset some of the potential future LGC deficit after the first year (which is how long I calculated payback). I reckon they won't be toast for a fair while yet.
Just my thoughts though. DYOR