You can open it up, but be sure to ground yourself to avoid doing any more damage (electrostatic discharge)..
Also, please read the corresponding repair guides, so that you would know what to expect.
Now that I think about it, the board may have a continuity problem somewhere, and the slow performance was due to an undervolted cpu. I don't know if it was a slow-acting short circuit, overheating, a flaking off trace, a burning out on-board component, etc. Maybe you can spot something with a magnifying glass, or not.
I really wish you luck with this, but your problem is definitely serious.
Back to the subject of photos, if someone will be able to do a dump of the memory chips (not the most fun thing to do, but may well be an option), as far as I remember, photos reside outside of cryptofs, so they should be available in their original form. Once you have the raw binary image of the chip's contents, there are tools like PhotoRec that scan for the EXIF data and extract the identified image files (no filenames though, those are stored separately and are rarely recoverable)