How to find my lost device if find my doesn’t work because it’s dead?

Start here:

Locate a device in Find My on iPad - Apple Support

Here is Apple’s advice for lost or stolen devices:

If your iPhone, iPad or iPod touch is lost or stolen – Apple Support

Use the Find My app to locate a lost or stolen device – Apple Support

If the Find My iPad feature was enabled prior to it being “misplaced”, then if active, you would stand a good chance of locating it. 

However, if the feature was not activated prior to being misplaced - or the iPad has been inactive or without an active WiFi or Cellular connection for more than 24 hours, the last known location will not be available - and the opportunity to use technical means to recover the iPad have been lost.

Without an active radio, an iPad has no method by which to communicate its location or interact with other Apple devices that are participating in Apple's network of find-my-enabled devices.

If the iPad can't be online to show you its location, you will have to just retrace your steps until you find it.

~Lyssa