Seriously, that ending caught me completely off guard. I'd spent the whole book convinced Liang Chen would find a way to break the curse binding him to the 'Black Chain,' maybe through some grand sacrifice or a hidden loophole. Instead, the finale has him making a different kind of choice entirely. He doesn't destroy the chain's power; he accepts it as part of himself and uses its connection to essentially become the new warden for all the dark energy it was leaching. It's a bleak sort of peace. The last scene is just him walking into the mist surrounding the ancestral shrine, the chains on his wrists not gone, but silent. It's not a happy ending, but it fits the grim tone. I was left feeling hollow, which I think was the point.
As for a sequel, I haven't seen any official announcement for a direct follow-up called 'Black Chain 2' or anything. The author, Yan Sui, seems to have moved on to a new urban fantasy series. The ending of 'Black Chain' felt pretty definitive to me—tying up the main character's personal arc, even if the world's problems aren't all solved. Sometimes a story just needs to end where it does.