If you can’t fly to grenoble you can fly to Lyon, not too much further and there are trains too.
To be honest if you’re looking to move about I would hire a car. Train connections are good from larger places, but then it’s buses to get up into the mountains. You’d be looking at a bus into and out of Alpe d’Huez, bus into and out of Morzine and a train from Grenoble to somewhere like Annecy or Geneva in between. Car would be a lot less hassle.
That said, if you want to pick the car up from the airport it probably limits you to flying into and out of the same place, as there’s often a surcharge for returning a car to a different location and it can be pricey.