Furthermore I expect that there will a way to move that data to a new device, even a new phone replacing a dead one. It's one of the reasons to buy a new one, it happened to me 2 times out of 3 since I had modern smartphones.
The safest and most convenient way would be an encrypted backup to Google Drive (for Android, I don't know where for iOS,) with a password that only the user knows, different from the one of the Google account.