If I use Pinsir's "Slow Crunch" attack and the Opponent's Active Pokemon retreats or evolves, is it still Knocked Out?
No. Evolving or moving to the bench removes all attack effects.
Source: Twilight Masquerade FAQ; TPCi Rules Team (2024-05-23)

Relevant cards

Note: All applicable cards may not be listed below.
SV6_3
SV6_3