There are a good number of threads on this. My suggestion is keeping a small amount of gas in the car if you wont be burning much. I think it is even recommended in the owners manual. I keep about 3 gallons in the car. The car knows the average age of the gas in the car, and will force you to start burning it off if its been too long.
The sealed system prevents the lighter fractions from preferentially evaporating, true, but it does nothing about oxidation of anything, more or less the "going rancid" of hydrocarbons. That's why the car forces you to use some once in awhile. It's a mixed bag.
The car takes care of this for you (good job GM Engineers) through Fuel Maintenance Mode. And Engine Maintenance Mode basically keeps the moving parts in good working order. I'll never see FMM, due to my driving profile and occasional long trips. But I'm about to see EMM for the 2nd time in my 6 months of ownership. Just rolled over 1000 miles this morning since the last time my engine came on.
As others have pointed out, GM put a fair amount of thought into this. The gas tank is sealed and pressurized to limit exposure, and GM specifies Premium fuel in large part because it lasts longer. If the average age of the fuel gets to be a year old, it'll enter fuel maintenance mode, as described in this thread:
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