Apple’s finally addressed a longstanding complaint from its users: being able to delete native apps you don’t use. The upcoming mobile operating system allows users to delete apps like Maps, Contacts, Calendar, FaceTime, and Music—at least based on the current developer beta out. And if you decide you want the app back, Apple has added these native apps to its App Store, which is similar to what Google has done with its first-party apps. Of course, there are some apps, such as Phone, which you can delete because it might cause issues with the device if you take them out. But being given the option to free up some storage and homescreen space is quite welcome.
Source: Apple Insider
It seems you don't reall 'delete' the native apps. They are somewhat encypted and taken off your screen, but they remain in you device. Downloading them again just makes them available again with all your preferences and settings.