Trade down?

who would have to be missing from the 1st round for the Saints to put more thought into trading down? for instance..... if Barkevious Mingo was gone but Jarvis Jones was still available, would we take Jones, or trade down? if they both were gone but, maybe, Star Lotulei was there, would we take him? who would have to be gone for us to decide to trade down out of the 1st round?