Apple has instructions for transferring an iPad to someone else.
There are all of 3 steps:
1. Back up your device.
2. Go to Settings > General > Reset, then tap Erase All Content and Settings.
This will completely erase your device and turn off iCloud, iMessage, FaceTime, Game Center, and other services.
If you're using iOS 7 and have Find My iPhone turned on, your Apple ID and password will be required. After you provide your password, the device will be erased and removed from your account so that the next owner can activate it.
3. Contact your carrier for guidance on transferring service to the new owner.
What to do before selling or giving away your iPhone, iPad, or iPod touch
So, again, if you want to will your iPad to someone, you have to give them the Apple ID account credentials and the decryption password for your iPad so that they can wipe it and activate it for themselves.
If you want to will some data to someone, that is a whole separate issue. There are about 1000 ways to do that, both using Apple tools and 3rd party tools. It has nothing to do with iPads or Apple ID's.
One way NOT to will some data to someone is to lock it up in an Apple ID account and not give them the credentials for that account. That is how you DON'T share your data. That is how you keep data private.
Every problem with a will has to be resolved in court. If a person has no will, the court makes all the decisions. If you say the deceased wanted to will you the contents of their safe but you don't have the combination and you want the safe manufacturer to give you that combination, you will need a court order. Safe manufacturers are not in the business of cracking safes for anyone with a heart-wrenching story. A court has to decide if the story is true and what to do about it.