Of course he will be shocked to see her. But will that make him stop loving Avni? I doubt it very much, or else this story has no point.
His Ek Tharfa pyaar for Avni has been a defining factor in his life. Probably the most significant thing that happened to him after Juhi's death. Nothing this big ever happened in his life before and that is why I think he felt he could never love again, so agreed for an arranged marriage.
The song Ae Dil Hai Mushkil signified to us that the feelings were from Neil's side from the very start. Of course Avni loves him now too. But I think she hasn't even named her feelings to herself, leave aside to Neil. He wants her to love him, that part is very clear.
Now the interesting part will be, seeing Juhi again (who probably still loves him), how will he feel? Because he's not sure his wife loves him but his Ex does. Neil kare toh kya kare? But I think this experience will clear to Neil once and for all that he loves Avni not coz Juhi is not there, but even if she was, Avni is still his choice. That should be the final conclusion to meeting Juhi again.