Yeah, it will be interesting to see what they will come up with in a few years. I also do believe something similar to the Mini will come back in some form, maybe not flagship device though.
This year is the first I haven't gotten AC+, in several years. The Mini is so small and most of the time I even use an ultra slim case with it. I don't feel I could let it fall easily. So now after your post I am thinking of what to do with the 13 Mini. I would need a monthly plan to have AC+ for many years which will get expensive. Around 10$ each month here. Or just get a battery replacement after 2 years. But what if it breaks... Hm... Off course you will get a Mini for certain even two years later brand-new. Apple will sell it till September 2022. Maybe even after that as they do now with the normal 11. I think this would be highly possible if the 13 Mini sells quite well. And even if they don't, resellers will normally sell such a phone at least one more year, sellout. So available till approx mid 2023 at least. Normally I wouldn't need AC anymore, only for Max phones because it is easier to drop them. Difficult.
Only thing I know, a Mini will be my daily driver for many years to come. If a new iPhone gets me very interested because of whatever I will buy it as a second phone, but the Mini is just perfect besides battery life.