Even if you don’t get new OS versions, you still get OS patches and security update for several more years. Also the App Store still seems to support devices seemingly forever. I was still able to download apps on my iPhone 3G seven years after I bought it. In terms of useful working life, these things are incredible.
Unfortunately you can’t download apps that the publisher removed from the store (EA Games, looking at you) even if you paid for them. If you don’t backup the IPAs (and/or don’t have a way to install them...) then you’re stuck. At least you can get a refund from Apple if you can find your iTunes/App Store purchase receipt.
No idea! But when I asked for a refund for my purchase of the iPad version of C&C Red Alert 3 (which I bought from the App Store around 2012) after EA pulled it around 2015 I contacted iOS App Store customer support who told me to forward them a copy of my App Store purchase receipt e-mail to get a refund.
