I work for a GM supplier (of services, not parts) so I guess I will jump in here.
The "employee discount" is nothing more than a temporary maketing program to clear out end of the model year inventory. They could have called it "biggest incentives ever" and it would have been the same thing. You really can get a good deal on a new vehicle and can see the pricing online at the gm website for vehicles in stock at your local dealership. And after the promotion ends, the employees will have their perk back all to themselves. FWIW, I don't care much for GM cars, I find them really dull and they have a tendency to add too much technology that breaks down a lot. I am a Mopar guy myself.
As for the layoffs, don't cry too much for them. Since the the timeline for this is 3 and a half years, most will be done through attrition. And I am sure if anyone is really laid off they will receive a nice fat severance package. And since people are still buying plenty of vehicles, just from different brands, these employees probably have a good chance of finding work within the industry if they want it. Don't get me wrong, no one likes that kind of uncertainty in their employment, and I have been through rounds of lay-off in other employment, but it is not like 25000 people are going to be thrown out of work tomorrow with no resources.