Offer enough money and he'll sign. But if he doesn't, I'm not so sure we should sell. We got £25m for Nasri purely because he was willing to stay in England. Nobody seriously expects Van Persie to stay in England if he decides to leave Arsenal - Barcelona, Real Madrid, Milan, Bayern whoever...they won't pay more than around £20m for a player who's 29 and in the last year of his contract. If that's the case, we might as well tell him to give us one more year and let him go on a free; not only to aid the development of the team and key young players like Wilshere and Oxlade who might be preparing to take over, but because Robin might single-handedly drag us into a CL spot - like this year - which makes up the difference of the £20m+ anyway.
From the fans' perspective, I guess we all want him to stay next year even if he doesn't sign a contract. Whether we lose him for £25m or £0, it only seems to go towards presenting some healthy profit figures. And we don't have to worry about selling any other big-money names because none would be left.