Allow you to open the app still and go through the menus, maybe you just want to export your data? Maybe you want to check the T&C again (which should be available offline from the menu)? Perhaps you wanted to see the design/ergonomics of the app before allowing it? It could be a thousand reasons. Photo app can display "No camera permission granted, click here to setup" instead of the visor or something, and the browser can also inform the user of the situation with a static page.

It's like proper exception handling: Do not just close the app, fall back gracefully and allow the user to retry.

I'd expect the browser to behave the same way it does when the device is in airplane mode: display a message about being offline, while still letting me play with the UI, adjust settings, navigate to local files and cached pages, and so on.

For the browser, view local HTML pages via file:// URLs. For the camera, look at previously-taken photos through the built-in mini-gallery that most support.

In the example of Kakao, it lists the contacts permission as optional and the app will install and open without it. But it won't let you past a nag screen without it first verifying that you have given it access to your contacts.

Really anything involving personal data should be up to the user. Especially something like your contacts.