Since your friend's parents do not understand the technology, I would simply tell them the importance of it, and that they preserve all of his belongings. They may throw the computer away or loose papers. So I would tell them to protect all the documents until you can search the computer and find the seed phases.
Hope that helps you a bit!
Many people do not inform anybody about they have Bitcoin because Bitcoin is not legal in many countries. For this reason a lot of Bitcoins was lost. Now there is only one way to inherit Bitcoin - to give a private key to the wallet.