How to delete data from dead iPad?

If the iPad is dead - as in it will not boot or switch-on - it is not possible to access or erase data from the device.

If iPad isn’t responding, do one of the following:

• On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
• On an iPad with Face ID: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.

If iPad still doesn’t turn on, or if it gets stuck during start up, see the Apple Support article If your iPhone, iPad, or iPod touch won’t turn on or is frozen.

If it is truly dead and the battery has completely failed? You don't.

Sorry.