Let's say we have a gas giant composed primarily of hydrogen and hydrogen-rich molecules that is ejected from its star system.
As this planet embarks on its potentially infinite journey out into the cold darkness of space, away from the light and warmth of its host star, what would happen to its atmosphere? Would the gasses freeze and fall, piling up as winds cease? Would mass be lost? Or would the planet just remain in a relatively similar state? I know Jupiter radiates more heat than it receives from the Sun.