In response to gamers' questions about the Marathon 2 (for PC) source code, VirtualWolf reports that this little tidbit was in the Marathon 2 (for Mac) ReadMe file:

This is the Mac source. The sole known archive of the Windows 9x source was placed in a lead box and shipped to one of our island laboratories for safekeeping.Unbeknownst to us, the boat carrying the box made an unscheduled run up the coast of Madagascar, where the ship's captain hoped to catch the end of the annual Miss Middle Of Nowhere pageant. The ship was approximately six miles from shore when it was torpedoed by a one-man sub purchased from the Hammacher-Schlemmer catalog by a punter with more money than brains. Divers are still combing the sea floor looking for the box containing the Windows code, and if we ever find it I'm sure we'll let you know. Windows hackers with lots of spare time may still be able to do interesting things with this code.

It's good to know that Bungie is making a conscious effort to find the code for interested PC gamers, and I'm still happy for you Mac users out there. Enjoy your new toy! ;-)