Sorry for the random replies, just had one thought, i had done what you did to my 3650 and how i recovered the MMC was by restoring a backup onto the phone and opening the MMC password file. At the time i knew nothing about where the password was hidden or could find anything online, so i was lucky to do it, but it was a backup which helped. Hope this inspires you.
Hope it works, let us all know if you recover the card, usefull for others to know if this can work again, if it does then good advise to everyone, KEEP a backup on the pc ;-)