What ultimately happened to the Huns?

In a similar way to Genghis Khan and his mongol hordes, after the leader of a tribe dies without central control most soldiers, as you said, would simply settle down and assimilate or slowly take the long road home. The reason why the huns are never mentioned again is because once Rome evaded seige and atilla turned around and soon died, the primary goal of their journey from the Danube was over. Unlike conventional large armies bound to a empire or powerful ruler, nothing was compelling tribal soldiers anymore to do anything. A new leader would rarely be accepted, and tired of pillaging and fighting, to settle down amoungst the ravaged western empire's towns and villages and start a family, would be an inviting prospect. You have to remember that spread out and disappated, the huns were like many of the Barbarian tribes living within the empire. Nothing worth of mention was ever achieved by the huns again, and so why fill up a chapter in a text book with how they found wives and built houses, or raised children and painfully tilled the land. That's just boring. In the case of the mongol hordes, their goal was actually achieved. They found pasture for their horses in western europe. Therefore they remained all over the place, leading quiet lives. All tribes work like this. Essentially, you were right.

You've got it - after the death of Attila thry returned to their homeland in Asia. As wit many other of the nomadictribes there, the gradually died out.