I don't think that Ash will use reserves. That was because BW1 can't featured old Pokemon and the league was a league prepard for BW1 indicated that the possibilities of reserves are very low although I wonder about some Charizard.
And of course, Ash is going to win against Trip. For me, I'm very convinced that Ash will defeat Trip in the league with a 98% of possibilities. I have a 95% of possibilites that Ash didn't win the league, of these 15% are for finalist, 35% for him be Top 4, 40% for top 8, 4,9% for be Top 16 and 0,1% for be lower than that.