Sagna is not likely to leave, simply because Eboue is quite likely to leave. But if they miss CL, I think if they get a good bid, and the player wants to leave due to higher ambitions, then they wont have qualms with selling him.
The players that i fear would leave us if we don't get into the CL are the players who have been at the club for a prolonged period of time and have become frustrated with the lack of trophies. Cesc, Van Persie and Kolo Toure. Or greedy bastard's like Adebayor. I believe we will be able to keep Nasri, Clichy, Sagna and the rest though. Gallas is leaving whether we get to the CL or not.