made a ticked and it turns out for the age my city had, if i have less than 50 diamonds for 30 days, city gets deleted....Apparently i had more for a very long time but once i spent some on my main world and went bellow 50 diamonds, my other city went under deletion. I gotta point out this rule is seems silly and its also not well advertised. I had to actually contact support before i find out how it works. I couldnt find page on the wiki and i assume i need to dig really deep to find it. You should also inform players whos cities are under risk. Age is pretty bad criteria for determining deletion grace period. I intentionally kept my city in Iron Age on this particular world, to see how much i can progress in all other areas and spent many hours. Had several well established GBs, i beleive i was at about 500k score already...well its a pity(yes they said its irretrievable).