I don't think Denly was ever being considered to open though, they had him pencilled in at 3 until he struggled in the warmups. Hence a possible vacancy in the squad for Roy, who they're clearly considering. Otherwise you're right, noone's done anything to displace Pope as the spare middle order player. Selection for the first test will likely be much more interesting.
When Archer becomes available is dependent on how much time he spends in the UK - if he goes to the Big Bash for two months he won't have completed the residency in time, but if he pulls out of that (which he has mentioned as a possibility) he'll obviously qualify quicker. You'd assume someone from the ECB will have had a chat with him recently. What the rules may or may not be on England naming a currently non-qualified player in a squad, who knows.