How to get encryption keys for "adoptable storage" in MotoG3 without root - alternate methods, anyone?

So my sister in law handed me her MotoG3 where some apps had mysteriously disappeared and the videos of their little puppy were all gone (the videos of their kids were not as important apparently). Her SD was formatted as adoptable storage, no backup of course... I spent 8 hours yesterday reading up on how adoptable storage works encryption wise (not in depth, but I know about the vold dir with key files) and doing non-destructive tests on the phone. I also have a Linux "dd" copy of the SD card so I can mess around as much as I like with that card. I do understand that in a previously rooted phone it will be no match to read the key file(s) but obviously her phone is stock. In a PC environment, I would boot with Knoppix or some other Linux rescue image on a USB stick to get access to the disk in a similar case. I just wanted to ask if this can be done with a phone (preferably not just "a" phone, but the MotoG3 :). Other ideas: The vold dir is in the /data partition and in my Linux/PC oriented mind, I have a delusional thought that perhaps one could install some "mini-OS" in the boot partition and leave the /data partition intact. That image could even have as its only task to copy the key files to a readable area or another SD card so no user-interaction would be necessary. Since no one has come up with this idea for the past 6 years or so that adopted storage has been around, I guess the answer is a big NO. Still, would anyone care to enlighten me as to why this is not possible or (still hoping!) suggest how this could be done! Decryption of AES128 (which the partition seems encrypted with) is "cumbersome". I guess there are no known "salts" that weaken the AES significantly that we could use to brute-force the encryption, or are there? As an alternate method, I guess the chip could be removed from the board or perhaps read while still attached with a chip reader, but that's over my budget and level of expertise. Also, for videos of a puppy, that might be excessive :) If anyone as more ideas, feel free to reply!!!