[TheLastSuperman]

I would find contact details and hate to say bother his wife... but some form of asking permission should be done since I assume (You know what they say about that so YOU need to do proper research not depend on my words here as I'm no expert on legal matters) any copyrighted work on his death would be transferred to his wife/heirs. Once a person dies who had copyright to said work, the copyright holds true for the life of said person plus seventy years after from what I've read.

I'm not 100% sure about all the aspects of this however if you changed domain while he was alive, simply contacting him and asking for a newly generated file/key would suffice but that is not an option now. I don't see an issue with you hiring a third-party for them to modify the files for your site alone but they can't "supply" any of the files i.e. re-distribute in any manner (assuming again) so they will need to edit the files you already own, on the server now and they should be fine modifying files you already paid for so the mods work as-intended. The way I remember his mod working though was by using IonCube and other to prevent piracy and that means the files are encrypted so how is one supposed to modify code they can't interpret? This was meant to connect to his site to verify licensing details if I'm not mistaken and to also hide his source code in some respects.