ipad removed email icon from start screen

If you have used search to insure that the Mail app is no longer installed, see the following from Delete built-in Apple apps on your iOS 11 device or Apple Watch - Apple Support

Restore a built-in app that you deleted

1. On your iOS device, go to the App Store.
2. Search for the app. Make sure that you use the exact name of the app. Find the correct name of built-in apps.
3. Tap to restore the app.
4. Wait for the app to restore, then open it from your Home screen.

Note that the exact name of the app is "Mail."

Have you tried a spotlight search for the Mail app? While the Mail app can be deleted, you can also re-install it. See the instructions for installing again here, Remove built-in Apple apps from the Home screen on your iOS 10 device or Apple Watch - Apple Support

It could be that you just moved it to another screen or folder. The search should indicate that.