Cesc Fabregas should go down as one of the greatest ever talents to have played for The Arsenal. He deserves to be up there alongside the likes of Bergkamp, Henry, Brady and Pires. He's genuinely world class, and once he gets his move to Barca, his reputation worldwide will grow and grow. He will not be forgotten so easily.
As for legend status.... no, but that's not because of his talent, contribution or effort.
For me, a legend has to have a certain amount of the right ingredients...
1. loyalty and longevity (Adams, Seaman, Bob Wilson (player and coach), Bergkamp, George, etc)
2. cult hero status (Bergkamp, Brady, George, Wright, Adams, etc.)
3. Ability (Bergkamp, Brady, Pires, Henry, Cesc, etc)
4. Memorable goals/moments (Wright, George, Thomas, Brady, Sunderland, etc)
5. Iconic teams ('79, '89, invincibles.... sadly, NOT the "Wenger Youth Project" era

)
6. Trophies
For me, Cesc just doesn't tick enough boxes yet, and if he leaves he never will
