I would think upper Junon is still populated, but likely less sparsely so, with the energy crisis/collapse of a major economic power causing a depression but they were never actually physically "ravaged" like Midgar was (there were definitely military casualties from encounters with both AVALANCHE and WEAPON, but I don't see any reason to believe there were ever major civilian casualties or damage to property. When WEAPON approaches there is shown a metal wall sliding over the foremost buildings like a shield, and I don't think that was ever breached).

On the other hand lower Junon is probably torn between being glad the water isn't getting polluted more (...UNTIL WE GO TO OIL, thank you Barret, Cid) and being annoyed at Upper Junon citizens down on their luck being arrogant and figuring that in these lean times they can pick up the fishing profession that has been lower Junon's backbone for generations. Leading to sometimes amusing, mostly disgraceful attempts at it, but when the fish were already being thinned out by pollution a number of Upper Junon people who figure out what they're doing in the water could easily cause issues with overfishing.

...I want a Case of Junon. I don't care it's not a character, this actually seems kind of interesting to me. XD