Cech - because he's the only way we have a hope of starting next season with a top class goalkeeper between the sticks. If we do come calling, and Mourinho has even a shred of decency, he shouldn't deny him the chance.
Hummels - leader and organiser; they're so rare these days, approaching his best years, could form an awesome partnership with Koscielny.
Schneiderlin - let Flamini and Arteta go and add a player that can play with discipline and intelligence, as well as play a bit.
Draxler - I know he's had more injuries than seems normal, but he's still so young and there surely isn't a better time to get him for a good price. He's got great ability, can play wide straight away but might have it in him to become a very good central striker if Wenger sees it in him.
I'd let Szczesny go and be a Number 1 at a lesser club, I'd also let Mertesacker move on, and let West Ham have Jenkinson, Arteta, Flamini and Diaby can all go, and I'd sell Cazorla too if Atleico Madrid made a big offer and possibly Walcott if he won't sign a new contract and a big offer comes in.
-----------------------------------------------Cech/Ospina
---Bellerin/Debuchy--Hummels/Chambers--Koscielny/Gabriel--Monreal/Gibbs
-----------------------------Ramsey/Wilshere--Coquelin/Schneiderlin
Chamberlain/Gnabry--------------------Ozil/Rosicky---------------------Sanchez/Draxler
-------------------------------------------Giroud/Welbeck/Akpom
All a bit fanciful but something like that is what I'd like to see. Although, the thought of Giroud up front for us for another season is not nice - I just don't see who there is out there though?