Just a quick question to confirm that in campaign mode ALL earned boons and burdens are kept and are added to the encounter, player decks, staging area etc. throughout the entire campaign? For example, if we earned Gandolf's delay in the first quest, that burden is still being added to the staging area when we hit Treason of Saruman ?

You will keep the boons and burdens until the campaign tells you otherwise. In particular, the campaign card for the first question in The Treason of Saruman instructs you to remove some boons and burdens from The Black Riders.

thanks for the info