Speaking as someone who has a lot of experience with NTSB investigations, unless it is relevant they will not care. Unless there is some reason to dig into the Tablet, it will be handed back to the owner. The NTSB maintains a very high level of professionalism.

Now the families of the decedent (worst case) will probably dig through the device looking for any recent pictures or communications.

The FAA could probably perform an electronic version of a PUBs check any time they please.

The tablet doesn't raise any additional concerns that your personal laptop does not already bring to the post incident /accident world. There are already ridiculously harsh penalties for digital content on a device which does not belong to the owner. Add to these concerns an inability to know whether the star of the show is age 17, 18, or there against their will. It is a level of legal jeopardy that anyone smart is not loading on a device that is carried past airport police twice a day.

I go by the Marine Corps standard, "if you don't like how she looks, turn off the lights."

Another true story ... in new hire training (back when Delta did not provide hotel rooms) a group of mechanics sharing a crash pad were summarily fired by Delta for circulating "porn of the day" across company computers. There was no warning shot. The first meeting was the termination. ALPA would defend us, but it's a dumb way to get into trouble.