You can switch to iPhone and keep on using Google, or you can switch to iCloud, Microsoft, or others as well!
Some people want to switch to iPhone but only for the hardware, not the services. For them Google apps for iOS make it ridiculously easy to log in and keep right on going. Others, though, want to switch to get away from Google's services and apps. For them, Apple, Microsoft, and others offer alternatives.
If you want to switch completely away from Google Services, you'll need an account with a different provider. A free iCloud account comes with your new iPhone, so you can easily try that and see how you like it. Otherwise, a free Microsoft account gives you access to a wide range of services as well. None of them have the scope of Google, nor the online excellence, but if you don't want Google, they along with a few others like Dropbox, can absolutely get the job done.
On the other hand, Google hasn't been as great about updating and providing truly native fit and finish on iOS, so you can get a better, more integrated experience with Apple's built-in apps, and just as good as Google, if not better, with Microsoft and others.
Here's a quick reference for Google services and apps, and their alternatives.
|iCloud Account||Outlook Account|
Again, you can absolute switch to the iPhone and keep on using all the Google apps and services you're used to. The iPhone, it turns out, is a pretty good Google phone too. If you want something different, though, if you want an alternative, Apple, Microsoft, and others can provide it. And the iPhone can be just as, if not more amazing, that way as well.
Apple even provides a Move to iOS app to get your started!