Spoilers ahead for people who haven't played the final games in the series.
From my perspective, the way they wrapped up the plot means that the story is essentially going to be a reboot either way. The original storyline involved relationships between several key characters and factions, including and especially Cortana, the Covenant, the Flood, and earth's government. And those plot lines are now all finished. Covenant gone. Cortana gone. The mysteries about the rings and such, solved. There is of course a new enemy that arose like a phoenix. It's an open-ended story that could go anywhere, but it's also essentially a new story with mostly new characters, so, a reboot in its own way.
The next game in this cannon will need to give us a reason to care about the new characters and factions, because the ones we have cared about so far are done and gone. So, what's it going to be? Roll the dice on making something that people will get interested in that won't feel like a re-hash of what we have already seen, or just give the old-but-proven story to a new generation of kids, with shinier graphics?
The second bet is clearly the safer one.