Github mirror: https://github.com/Jackathan/MarcLaidlaw-Epistle3
Edit: Fixed now, and the title changed.
I also suspect that if no game is going to be released, Valve will not bother with legal action; they look bad as it is already.
In that spirit there's probably a good argument to be made that it's in the public interest to add to clearly incomplete bodies of work that appear to be abandoned. Whether that's practical or does more harm to the public good is the question.
Also they owe you for the thing they made already. If you forced them to complete works on your timeline then you're indenturing them.
.. Ha-ha, 2 downvotes and no explanation. Is this about so-called 'copy right' bullshit?