I've been weighing this up all week and changing my mind daily and genuinely could tick any of those boxes.
I'd hate to lose both for free because next summer could only be a downer no matter who we sign, and knowing Arsenal it'll weaken our 2017 budget and probably our 2018 budget too. At the same time, I wouldn't the want the hit (PR, morale and football) of losing both this window either so I'd say ideally it's one stays one goes.
In terms of which one to stays, who knows. Depends what the offers are for them and the state of the player. If one is more likely to extend their contract I'd happily gamble on that. Football wise, Sanchez looks likely to be our top scorer in a season since RvP's exit and Ozil has been our best creator in a season since Cesc's exit so they both have merit for me.
I'd maybe accept having to lose both on the basis that we 1) got good fees for them, 2) they really wanted out and 3) we had the transfer window to end all transfer windows where we show the world we mean fucking business. Take our 80-100m budget, add in what we recoup, maybe shift someone like Ramsey and/or Ox and then blow 160-200m on exciting players aged 18-26 and really try and rebuild a new project for the next 4 years because patching up this team isn't going to cut it anymore.
Keeping things consistent hasn't helped us so I'd rather get half a new team. GK, LB, CM, winger, Alexis replacement and/or Ozil replacement to go straight into the first eleven. Wenger likes to not change too much too soon with his squad, but I bet he'd have more joy trying to play the kind of style he wants to if he brought in a load of players actually capable of doing it. I'd accept Szczesny as the keeper for one season if we want to take that gamble then re-eveluuate in 2018.
Then again, we could basically do all this and keep one of them too but spend 130-170m instead so who the fuck knows.