I actually believe the Dragons excel, or are even the source of, the God's powers. It wouldn't be too surprising that, for me, the Gods left Tyria because of the fear of dragons, or for fear of reprisal. Or maybe just genuinely because they had bugger-all left to do. Who knows?
But here's a thought, that might suggest the rise of the original Gods... What if the mortals once slayed a dragon? Or at least put them into their hibernated state? In almost all cultures there's a slew of dragon-slaying tales, and it's a big part of the fantasy genre for that reason.
And if dragons would happen to rise once more, that a new group of heroes should rise to defeat them isn't too hard to imagine in the greater scheme of things.