Only if necessary. And by that, I mean at the end of Ash's journey. I'd do it like this:
Ash has finally reached the Final of a Pokémon League Tournament in Region X. He's locked in battle with a fiercely tough opponent. Pikachu's his last pokémon, is really struggling and can't overpower the opponent, who has one or two pokémon left. Pikachu limps back to Ash, and attempts to retrieve the Thunder Stone from Ash's backpack. Intimate moment with Ash and Pikachu, some screenshots of all the struggles they've overcome as "Ash and Pikachu", not "Ash and Raichu". Ash encourages Pikachu back into the battle, Pikachu charges forward, jumps into the air as Ash, holding up the Thunderstone dramatically, commands "Pikachu, Thunderbolt!", Pikachu sparks from his cheek, and glows slightly. At that exact moment, you get one of those dramatic freeze-frame/artistic panels they've been putting in the Sinnoh League (i.e. the one after Ash's battle with Paul) of Ash and Pikachu in their respective poses. Then the credits role (possibly extended ones featuring the original series' theme tune as well).
Yeah, I've been overthinking this.