Earlier quoted context omitted.
I don't believe it is as bad as BoorishBears says. Yes, configuration changes cause a tear down and recreation of your view/controller layers, but there are several patterns to deal with this cleanly (view controllers whose lifecycle spans multiple instance of a view is one of the more common, with the view instances detaching/attaching as they come and go). If you use a Flux like pattern for handling application dat…
Don't get me wrong, I don't mean to imply writing clean apps is impossible but I believe it's a fair assessment of the "state of the Union" for development. Even your comment kind of alludes to the mess: Yeah there's RxJava but it doesn't inherently solve the rotation issue because your Observables so you still need to persist the information needed to recreate them. And any long running tasks need a separate solutio…
However, I don't think that in the end it's that horrible, once you overcome the learning curve.
If your process is killed and the user returns to the app, you have to be able to restore state from either the Activity's saved instance state or from some other form of persisted state anyway - whether the current approach to configuration changes was in use or not makes no difference here, it's due to the entire approach of the OS to killing and restoring processes as required (and I believe this same approach is used on iOS and for UWP Windows applications).
For handling of async results - once the owner of an async operation is not tied to a single instance of a view and is instead tied to the overall lifetime of that part of the application (e.g. retained Fragment, a Conductor controller, or pretty much any other reasonably modern view composition library), it's pretty trivial to handle. You're guaranteed that nothing else will run on the main thread for the duration of an Activity destroy/recreate cycle, so you don't need to worry about being in some unknown state. If the view was recreated due to a configuration change, rebind your view model/s when it attaches. If you're being torn down because the user left the retained Fragment/Controller/whatever the operation was tied to, you'll receive an indication of that and you can either send a cancellation signal (e.g. unsubscribe), or if that's not possible, have an isDestroyed check where you receive your result to ignore it. If you're on the back stack and still alive but have no view (i.e. view NPE), don't bind your model immediately - update your view model, and the same code you use to rebind on view reattach will kick in when the user returns and a new view is created and attached.