Does Ash ever re-encounter his Butterfree after the Butterfree's Goodbye episode?
A simple answer is no. We don't see Butterfree and Ash ever meeting again after their farewell in Bye-Bye Butterfree:


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                    A scene just before butterfree's departure 



As mentioned on the Bulbapedia (and partially in the comments):



  Ash's Butterfree has since appeared in the tenth opening for the anime, Spurt!, along with his mate, the pink Butterfree. 


  However, he has not returned in any episodes since his last appearance. Ash has, however, flashed back to having him several times, such as in The Thief That Keeps on Thieving!, A Trainer and Child Reunion!, and Butterfree and Me!.