Here are my strategies for dealing with the dragons. I know some are rediculous, but we'll have to decide.
1) Get one or more to join us. This might mean befriending them, or it may mean joining them as their priest in order to get them to turn. Fair warning, when we run into our first named Dragon, I intend to have my guy grovel his ass off and offer himself as a servant. I doubt it would work, but he'd rather be a slave than dead, and he'll turn on the dragon later anyway.
2) Weaponize the shouts. This would mean a huge shift in the Grey Beards, though, as we can't learn in time.
3) Turn the armies against the dragons. I doubt one of us could get Tullius and Ulfric to sit at the same table, though, so maybe trick a dragon into attacking them both, giving them a common enemy?
4) Draugrs. That is all.
5) Can giants be reasoned with? If so, it's worth a try.
6) Elder-scroll time travel thing. Heroes from the past.
7) Send Alduin to Oblivion. Might trap him for a while and by us time.
8) Get a god or, failing that, Daedra Lord to take Alduin on. No idea how to do that, and even Sheogorath isn't crazy enough to try.
9) Sovngarde travel + Heroes, because we're getting desperate.
10) Try to make a Dragonborn. Any theories on how to do that anyone? I know it would require someone to absorb a dragon's soul.
11) For the really desperate, obscene numbers of summoning staffs.
12) Keep fighting and hope we aren't all eaten.
Yeah, I though about it too much, and I doubt we'll do any of them, but just in case...