Don't go trying to put a happy face on this.
Spengler is NOT putting a happy face on it. In fact, after observing how aboriginal cultures today have higher suicide rates even among the young, he makes this observation...
Spengler’s Universal Law #2: When the nations of the world see their demise not as a distant prospect over the horizon, but as a foreseeable outcome, they perish of despair. Like the terminally ill patient cashing in his insurance money, a culture that anticipates its own extinction has a different standard of rationality than does conventional political science.