This doesn't need to be preserved (unless people specifically want it DRM-free), Steam recently released all three games in the series for free. But still, for the sake of DRM-free release, I support it.
I don't have a personal memory of Marathon, it was slightly before the peak of my gaming era, but it was the precursor to Halo, one of the all-time legendary and iconic FPS games of the last 25 years, so it definitely deserves a place in history.