Some of these questions are very easy to answer. In relation to the future of dealers and spare parts, there will be Hyundai/kia/Toyota dealers with Holden spares available through their spare parts departments. That's been the system for years at Holden dealers where other brands were secondary. The tables are simply reversed. Those dealers that survive the blood letting are those with multiple franchises. Some might be scrambling to establish them about now but might have left their run too late.
Future of GM in Australia? Non existent after the end of this year. No more US models then. No Arcadia or Equinox. No Chev Camaro or Corvettes because GM wants out of RHD markets. As for the Colorado, I'd suggest it dies but we get the latest MU-X sold as Isuzu. Trax, gone. We wont get the replacrment model. I reckon the Isuzu will be the only vehicle with any connection to Holden that will be available.
I thought we would end up as GM Australia, but not so. It should mean the Holden name and logo is available for any interested buyers of Oriental origin. Holden by Long Dong Motor Company anyone?