Looks like Halo PC won't be dying after all.
A Bungie dev stepped up and worked with the Halo community to develop a patch that would route Halo PC to a new master server Bungie set up to take the game off the sinking ship that is Gamespy's middleware. Here's the petition that probably drove it to fruition, and here's the forum post with the patch updates.
As one member of that forum noted, "You know, I can respect a game that has players just refuses to let the game die off. That to me shows how much the love of a game there is."
EDIT: Seems Halo 1.0.4's still running. I guess all versions were handed over the Bungie. I figured they'd let the pirated versions of HPC get shitstomped, but I was wrong.