As an aside, what moves me most over the Arthur story, is the belief that he will return in the time of England's greatest need. And I also hearken back to that Romanised Briton (Arturius?) who was so key in the fight to stem the Saxon tide
Lee beat me to a response to this, in the thread Kees just started about the allegorical Christ figure resembling nature and nature gods in the eternal circle of death and re-birth, but there isi also one more interesting point here, that possibly includes the figure you've mentioned above.
In "Prayer Magic and the Stars in the Ancient and Late Antique World" by Scott Noegel, Joel Walker and Brannon Wheeler (a good read so far - almost half way through) there's an idea raised of "the wrong god" being in power, when a country has been invaded. If the ruler has been deposed, and often the ruler is connected to the local divinity, or is allegedly divine himself/herself, then the god/s might also be seen to have been usurped in the heavens by those of the new ruler.
I've given this some thought, and I suppose it might also stand to reason that should the god be reinstated it would be a return, almost a re-birth, and perhaps any living man/legendary man who was responsible for defending his country (and therefore their god) or overthrowing the enemy, would be seen as a crucial link in this chain. To add the element that this figure could return from the dead in times of need seems an inspiring extension to this idea, do you think?