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You don't say what device you have.
Never worry, it won't be gone. Many people have these issues with Phone or Contacts icons swiping off the dock or homescreen.
Go to the App drawer / list and find the Contacts icon or People icon, hold and swipe it to a homescreen space, and then swipe it down to the bottom dock.
If you can't find it you still have options.
The Phone / dialer screen normally has a Contacts tab, or start typing a name in the dialer and it should fill in.
Worse scenario, go to Settings - Apps /Applications Manager (Samsung) - All column, scroll to Contacts or People app and check everything on the App Info screen. If it's disabled (unlikely) it would be in the Disabled / Turned Off column so tap it there to enable it.
If this doesn't cover it, register back, or if urgent start another thread