I was an Olds, Pontiac, Buick raised kid in that order and it broke my heart when the first two were killed. I always thought the same as
@Somedevil that the Pontiac/Olds combo would have been tight.
It's a hard piece of auto history because they were always GMs "excitement division" and they never really let it be exciting. Take a genuine look at the Fierro, the 88 GT was America's first real midmounted sports car. And is it ever fun to drive! But almost every iteration before then was what everyone remembers.
There would have to have been a model honeymoon for the new owners on the models available, so they could start their own lines. Either continue on with the new model branding of G8, G6, etc, with the aim to use those successes. I imagine GM would be open to an engine deal, at least starting out.
I got to drive a G8 gxp and it was one of the few times I was a really pressed back into my seat. Most automags were putting it in the same level as the 5 series. Gm again under sold its potential, because what driver wouldn't want a RWD V8 that made BMW nervous?
There were also plans for using caddies roadster frame for the next gen G6, which would have made it a hell of alot sportier. Thats a route worth looking at because it could have been an import fighter, I was always shocked by how good it was on gas, and I liked it's stylings.
And introducing a midmounted sportscar would be key I believe, and maybe... A partnership with the company in Tampa that does "Trans Am" conversions to catch the retro muscle car wave.
This also seems out there but I would also reintroduce the Aztek, the Breaking Bad hype could have been a coup if GM management weren't habitually sticking their collective heads up their arse. Some light restyling, and fixing the visibility issue, because the blind spots made it a task to drive, I'm 6' and struggled sometimes changing lanes with lower cars beside me.