Stuck on guided access on iPad with no home button to do a reboot

When you are stuck in Guided Access mode, you can be really stuck as the typical triple tap on the home button to quit out of Guided Access may not work. Even a forced exit won't work because the power button and the home button are disabled. 

Devices without a physical Home Button

For iPad’s without a physical Home button, you’ll need to follow a different button sequence…

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.

Use Guided Access on iPad - Apple Support

Use Guided Access with iPhone, iPad, and iPod touch - Apple Support

See especially the second sentence.