There are decompilers known to exist, created by members of the community, however, they do not share them. I think one of them did decompile games, if you could have proved it was your source.
However, even if the source was decompiled, it would look nothing like the program some one originally wrote. It wouldn't even look like DM in most cases.
If you want to know how to do something you see in another game, you could always contact the owner.
Or potentially look for a demo by using the search feature.
XD I actually have tried to make an extractor but then again I am only 14 and I want something to work off, I am not really the kind of guy who takes 6 months making a game.
Quick BTW:
If i did get someone's source code from a file in a .dm files and there images, I would keep it (I am not hiding anything) and I would make me the owner so I know what its like to be an owner ;D
I feel you'd be much better off designing your own games.
Try out some of the demos, and don't just copy and paste.
Actually examine the code, play around with it and see what makes it tick!
Then try to incorporate it into your own game.
Using ripped sources is like getting advise from a primary school teacher instead of a college professor, you just don't do it! :)
However, even if the source was decompiled, it would look nothing like the program some one originally wrote. It wouldn't even look like DM in most cases.