Although saudade isn’t exactly what you’re looking for, it’s in the ballpark – one of those words that doesn’t truly translate to English, but encompasses the concept of longing for something fondly remembered that is now out of reach and may be eternally unattainable. I’m thinking an exemplar would be a Cuban who left his homeland when Castro took power and misses the country, but realizes it’ll never return to “the way it used to be” even if the Communist regime were to be overthrown.