There is a little known clause in Actors Equity contracts that if a production "moves" to a smaller venue, actors must still be paid their original salaries. Broadway AEA salary-minimums are indeed higher than those Off-Broadway. So any of the actors who performed in the Broadway run (and I believe at any time in that run) are legally entitled to that same salary if the show transfers whole to New World Stages.
Note this would not be true in the case of a "revival", in other words a whole new production built from scratch. But if the "new" Avenue Q is judged by AEA to be the same production merely "transferred" then the rule should apply.
Of course, if the Q producers simply hire an all new cast...then I assume they can hire them at Off Broadway rates.
UPDATE: Well, whaddaya know: AEA bows to Avenue Q producers.