If Pikachu isn't in the match, it should be removed for the sake of a Pokémon that needs more screentime, and that's not Infernape. If the writers want to keep things familiar for viewers that have only watched the DP series, they need look no further than Pikachu.
Mach Punch hardly makes Infernape the ideal choice for a counter to Darkrai; Infernape is also completely helpless against Dark Void. If anything, Heracross is the ideal choice and that is why it is being used again, but it will probably not defeat Darkrai as that would make the battle boring.
Quilava is the obvious choice here due to its untapped potential and its association with Bayleef and Totodile, but since Noctowl would be quite useful against Darkrai, it could (and arguably should) take Muk or Pikachu's place. As for Donphan, I can only see it being used if the team consists solely of Johto Pokémon.
Well Infernape would be the ideal choice if Ash has a Sinnoh pokemon in there. I wasn't talking about in general. I was just thinking that if the writers want to include a Sinnoh pokemon to battle in the match (since it is Ash's last league battle), I was thinking that Infernape would be the choice.
And I was thinking Pikachu or Infernape because I could see them lose the battle for Ash. The other reserves don't need to be the last pokemon to lose. Pikachu seems more likely but again, if there is a Sinnoh pokemon in there, I could see Infernape be the one to take the loss.
But we'll see, I mean we don't even know if we're gonna get another skipped battle to compensate for the other unused reserves. I mean at least one that shows 3 pokemon. If it only shows 1 pokemon like the Snorlax battle and assuming the writers want to use all the pokemon in the opening/DP 182, then Heracross is the only reused pokemon.