Tom
I think the contract with the NSW (Sydney) government runs until 2016. Until then the Open is in Sydney. The major golf events in Australia (Masters,PGA, Perth International, Open) all survive because of state government sponsorship.
Most likely the Open will be in Sydney so long as the local govt. puts up a significant part of the money.
If it wasn't for the provincialism and 'branding' cities with events we could alternate the Masters (Melbourne) and The Open between Sydney and Melbourne. That would be a better way to do it.
The Open was best when it rotated around the five (six if you count 1971 in Hobart,Tasmania when Nicklaus won) major capital cities. That arrangement finished in 1974 with Gary Player winning at Lake Karrinyup.