Ah, the bane of all adventurers: planning. Why waste time with thinky-think when big stick already hit good?
Though our party of three didn't include any ranged weapon characters (and my druid was the only caster), so we'd have been completely screwed if the dragon didn't fail a save before I ran out of spell slots. A strength save, so our own "plan" was a stupid gamble that only paid off due to luck.