This is what I think will happen:
(1) If Arsenal finish outside of the Top 4 this season, then Wenger will look at his own performance and say it's not good enough and he'll walk. We'll probably appoint an interim manager from within the club to hold the fort, whilst the club work on his long term successor
(2) If Arsenal do finish in the Top 4 then Wenger will stay for 1-2 more seasons and announce that it is his last contract, and the club will work on his successor in earnest.
I could be wrong, but I think this is how Wenger and the club will manage the situation.
(1) If Arsenal finish outside of the Top 4 this season, then Wenger will look at his own performance and say it's not good enough and he'll walk. We'll probably appoint an interim manager from within the club to hold the fort, whilst the club work on his long term successor
(2) If Arsenal do finish in the Top 4 then Wenger will stay for 1-2 more seasons and announce that it is his last contract, and the club will work on his successor in earnest.
I could be wrong, but I think this is how Wenger and the club will manage the situation.

