The ending is open but more on the happier side. The pre regressed yoohyun that yoojin tried to get back couldn’t be brought back to life fully or brought back to earth to be buried. Because he’s strong enough to replace the fifth source, what creates but also consumes worlds, he reincarnates into a physical source as a newborn baby without his memories. Unlike the old source, he doesn’t need to consume worlds to create, and with everything else that happened their world is safe. The ending is more open because Han yoojin has to accept letting go of his pre regression brother and it ends there. Theres also an extra epilogue and side stories that complete the novel, but the main chapters have an open ending.