Keystore backup

I had quite a hard time to create and understand the process behind a keystore. I think I got a clear picture now of how it works, but I would like to know:

what will happen if this keystore is lost?
how should we backup a keystore?

This has got to be one of the most frustrating things that I have ever experienced working with a technology. I perfectly had my app presentation setup on the App Store. I installed Visual Studio for Mac and updated Xamarin Studio and then all of a sudden my SHA1 fingerprint no longer matched the Google Playstore. When I try using my backup keystore file, Unity gives me a build error. Everyone is saying to have a backup of the keystore but nobody knows how to restore it and build an APK using the original SHA1 fingerprint.

I am worried what is going to happen when I get a new machine. Am I going to have the same problem? I really feel for developers that have thousands of paid users and can’t post updates. I never had this type of issue on the Windows Phone marketplace. Extremely disappointed in the App Store.