If I use Ribombee's "Plentiful Pollen" attack, do I still get to take 2 more Prize cards if the Defending Pokemon is switched out and then I KO it next turn?
Nope, if the Defending Pokemon is switched with a new Pokemon or evolves the effect of Plentiful Pollen goes away.
Source: Temporal Forces FAQ; TPCi Rules Team (2024-03-21)