Are you thinking of selling it because of the discontinuing rumors or because you've get tired of the bag design?
In the last case, I'll recommend you to sell the bag, even if the resale value isn't amazing (a little money is better than no money at all). If you don't wear it, no need to keep it in your closet.
The rumors about the City being discontinued are up for 4/5 years now. The production has decreased but they are still selling them in stores. My local SA told me it was still rumors at this point, since AW 20/21 featured some City bags and the prices of the City bags are increasing. For example, in France, the nano City was 950€ in summer 2019 (1190€ in March 2021), the mini was 1150€ (1390€ for the regular version, 1690€ for the graffiti version). New iterations of the bags are up every year.
If you're selling it because of the discontinued rumors, but you like it anyway... My advice would be to keep it