While I firmly agree with the copyright infringement issues that arise from decompiling mdls for Gmax, apparently there is a programme out there that does this, an acquaintance of mine has done this (with author permission) and it worked I believe. If there is express interest in it, I can find out the name, although I am not sure what the general consensus is on it, and perhaps if it is best left nameless...
Although I was just thinking, even if you could get the physical mdl into Gmax, you would still not be able to re-compile it with the exact same xml code it was originally compiled with (think custom animations) unless the author supplied it to you, or you rewrote it according to your needs.