A hard reboot of the iPad will close everything.
Hold the power button in until the power slider appears.
Your iPad must be special... I just tried it on 3 different ones simultaneously... iPad Pro, iPad Air, and iPad 3. The first two have the latest iOS on them, the iPad 3 has the latest 9 that it will support.
Tried it by holding power buttons until slider - then slid it to power off. Came back up... Master Fader still running when I double pump home.
Then held powerbutton and home until reboot.... Same apps running.
Every single time I have had an app lock up (happens A LOT with the mail client, at least once every week or two) - I have to double-tap home and close out the app, then restart it and all is well. Rebooting 10 times in a row won't even help.