A whole slew of empires (German, Japanese, Ottoman...) were destroyed after starting/entering WWI or WWII, losing everything in less than a decade. Did anything like this ever happen in the period before modern weapons or transportation?
Did any pre-modern empire ever attack a neighbor fully expecting to win, only to find their empire fully conquered/destroyed by that enemy shortly afterward?
Khwarezmia was a thriving Islamic empire in Iran with a foothold in central Asia; when they killed Genghis Khan's emissaries, the Mongol invasion completely obliterated the empire in the space of about three years. Massacre and mass enslavement were common tools for the Mongols; a half dozen of the largest cities in the Empire were wiped out during the invasion, in less time than it took the empires lost to WWI.
While stretching it on the idea of pre-modern (since it's early modern) and stretching the idea of Empire, the dissolution of the Holy Roman Empire is attributed to the Habsburg Crown pursuing and declaring war on the First French Empire in 1805.
In 1804, Napoleon was voted (which was completely legal and legitimate), the Habsburg crown unified the various Kingdoms and lower crowns into the Austrian Empire, but still continued as Emperor of the Holy Roman Empire. Interested in punishing the "upstart" Emperor, the Habsburgs invaded the Duchy of Bavaria, violating their sovereignty which was protected by France. In a very quick series of events, the Holy Roman Empire was dissolved after disastrous defeats at the hands of the French. The dissolving of the Empire was a requirement of the Treaty of Pressburg As such, this would be the closest to a pre-modern Empire being destroyed.
The Dacians did not have an empire, but they did overestimate their chances against the Romans and ended up regreting it.
Ancient Lydia is a classic example: it's King, Croesus, asked the Delphic Oracle if he should go to war with the Persians (Cyrus the Great), and the reply was something along the lines of "if you do, you will destroy a great empire." Oops. The fall of wealthy Lydia to the Persians was a huge event in the Hellenic world.
The most typical example of this is summed up in three words: "Carthago delenda est". Carthage must be destroyed. Cato the Elder was far from the only advocate for the destruction of Carthage, but he was certainly the most prominent. The Third Punic War was basically just an excuse to do exactly that, once the indemnity payments from the Second Punic War were completed.