Can this vane prevent/delay wing stall?
This is a very good idea and has already been done. It is called a slat and is positioned ahead of the wing where it will do a better job of turning the airflow and not causing the slat to stall, as shown on your diagram. Slats allow a 10-12 degree higher angle of attack before the wing stalls. Fixed versions in this more forward position have lower drag in cruise. 



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The reason a more forward placement is superior can be seen in the streamlines of the airfoil at high AoA. The inlet gap between the slat and wing is located right at the airstream stagnation point. This is where air pressure is greatest, enhancing the operation of the slat.



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