What's next? Hmm, let's view this from the neutral, aka obvious view.
Update's still coming out. Wouldn't update a game planned for cancellation.
While Rarebit was probably the biggest cog in the MxO Dev machine, he definitely was not the only one, although judging from a severe lack of communication, it's hard to tell if 9mmfu isn't just extremely busy now that his workload is that much greater or if he's also quit. Either way, somebody has to run the show... right? Might be a low-paid intern hired on just to handle basic grunt work of updating mission content. Could be nobody, and this last update will be The last update, after which corporate bigwigs will wait for the community to slowly die out due to lack of anything before they can safely pull the plug.
Rarebit's depature, while sad, was foreseeable (and extremely obviously going to happen), and whatever plans he's left behind are sure to be followed, and when those are run out, we'll all see what we'll do then. We move on, like always.