I also have the feeling that Denilson will not be sold in the summer (Al and Rosicky will) but, that is more down to the fact that Wenger would want to give Coquelin/Frimpong a chance and getting a good defensive midfield player would "kill them".
At the same time, he can't expect them to be the first back up because of their lack in experience. So, he'll keep Denilson there and give these two a shot to overtake him based on their performances. Once/if one of Frimpong/Coquelin (mostly Frimpong) is clearly ahead of Denilson in the pecking order, he'll be sold.
Kinda similar to what happened(or is going to happen) with Almunia.
New player is not brought in because the manager trusts the youngsters. But, the pathetic old first choice is retained, in case, the young guys don't fit in/are not good enough. But, this would actually work only if Frimpong/Coquelin actually turn out to be good like Sczesny/Fabianski did.
I think, Wenger would observe both over the pre-season before taking the final call but I also have the feeling that he'd finally decide to not buy.