The Sonic is here to stay for the foreseeable future. Gamma II will become G2XX soon and there will be a G3XX afterwards with more variations of the platform than there are today. There's plenty of room for Spark, Trax, Sonic and more.
Delta II, or D2XX (later D3XX), which underpins the Cruze, is also here to stay. GM realizes that small cars and CUVs are a good place to invest money and the coming Equinox is on this platform.
G2XX - Minicars, Subcompacts - Spark, Sonic/Aveo/Barina, Trax, Encore/Mokka, next Corsa, etc.
D2XX - Compacts - Cruze, Astra/Excelle GT/Verano, Cascada, Volt/Ampera, Orlando, Equinox, Envision, Terrain, Antera, etc.
Anyone else hear that GM is ceasing its partnership with Holden, Australia in a year or two?
Not happening. Holden IS GM. What is happening is that Holden will not be producing cars in Australia any longer. After 2017, nobody will be building cars in Australia. Holden will import Chevys, mainly from South Korea, and sell them to Australians and New Zealanders as Holdens, much the way it does today. The only "real" Holden left is the Commodore and production ends late 2016. I'm hoping that GM will build a Commodore on Omega and export it from here to there.