Since the SDK is never going to be released what would be the harm in decompiling DM's code and ghetto rigging it through some C++ platform? or whatever the game was coded in? I know that people have gotten around games not have development kits to make mods but I am unsure of the method. Surely there is someone out there who knows a little bit about this, or someone who knows how to do something like this with an interest in DM?

This is definitely not the right place to be talking about this. That and the fact that it would be a wee bit too hard to do this.

It would be easier to spend years redoing the game as a HL2DM mod than trying to decompile a whole engine like that. There might be ways to make slight modifications using some methods... But sadly it wouldn't do much good.