Don't think we can. This community was built by fans of Bungie, and Bungie's Halo. 343 has taken it in a completely different direction, and while not objectively a bad thing, the active and prominent members of the community left after seeing that 343's Halo was not the Halo that they loved.

The handful of folks that remain from that group are here because they enjoy 343's Halo (or at least enjoy some aspects of it while hoping that 343 can live up to the established legacy that Bungie left behind), or because they like the people in the community that remain with them. We aren't going to reverse anything. That's up to the new folks who discover 343's Halo and decide that they enjoy it enough to seek out smaller fansites rather than the Waypoint forums (one of the reasons that HBO became so popular was because in the old days, Bungie didn't really have an organized forum and community focus, which was something that Claude and friends worked hard to make a reality; hosting videos, contests, fanfiction, fanart, etc.), but these days those sites handle more stuff than they once did.
Who is submitting fanfiction for 343's Halo? Who is submitting art? Who is having in-depth debate regarding the universe, games, or community? None of that happens here anymore. There is no Randall Glass for this generation, there is no Red vs. Blue, there is no High Impact Halo, no Leviathan, Yet Another Halo Comic, Stuntmutt, or Rockslider (wait, scratch that last one) for this generation...

If HBO (or H343O) is to become even remotely relevant again, it needs new blood. It needs people who take what 343 has given (and will give) and make something of it. 343 has done a less-than-stellar job of giving folks the desire or tools to do so, but their own community lives.

The HBO of old isn't dying, it died. It simply doesn't exist anymore, even if a handful of the people-of-yore that cared about it are still around. With BSangel's leaving, that list got a little bit shorter.

Not a bad thing, per se. But it is what it is.