Theoretically there's some good value, but it depends on to whom you're selling. We'll get £4-5 million for Szczesny in Italy if we're lucky. We'll get more in Premier League but we still need to find someone in need of a goalkeeper, and it has to be a club that Szczesny thinks is worth the time. He won't go to Sunderland like Mannone did.
Walcott we're probably stuck with. He rejected talks with Leicester which means he'll also be likely to reject West Ham, Southampton et al. We might get lucky and see City or United bid for him in an attempt to increase their homegrown quota, but it's a long shot.
Debuchy won't fetch many coins either. I can see him go back to France for a million or two; we're probably willing to let him go for a nominal fee just to get him off the wage bill. And Chambo will probably go on loan somewhere.