When a new expansion comes out (descent of dragons, etc) do the old solo adventures get their card pools updated. For example, would i be able to find a galakrond card while playing tombs of terror?
Yes. In Tombs of Terror you can find them in Bob’s tavern. In Dungeon Run new minions may be offered in Unique card buckets of Mage, Priest and Warlock
Not necessarily; you can get DoD cards via Bob’s Tavern, Discover effects, and random addition effects (i.e. draconic lackey from lackey supports), but they won’t be included in the normal buckets after each Boss.