Mail icon to on iPad desktop disappeared. How can I get it back?

Swipe from screen to screen and look for it in folders or on other screens or go to Settings>General>Reset>Reset Home Screen Layout.

You're welcome.

On the Ipad Mini 2 you open Apple Store icon. In the "search" you put "mail" and click "open". But as your question is 2 years old - this answer is for the new owners of Ipad Mini 2.