Cattlin 2.5 years mine-life, page-32

these are the figures from 2012. They didn't revise them because they shut down production 2013-end 2016. By your own quoted figures, assuming those assumptions are right you would be more accurate to commence the '4.5 years' from February or March this year. They wouldn't have needed to mine too much of the ore body before then because they had all those tonnes of tailings to process and processing rate was below nameplate.
Regarding comments of the cut-off OPEX for the ore, the assumption that 50% of the is unreachable is a bold claim IMO unless there is a statement out there of notoriety to support that claim.
In terms of price opening of some competition will drop the price a bit but to the point where it overtakes OPEX would need to fall further than literally any price projections I have seen.