So I looked up the Torchic line's learn sets. If we never evolve Torchic to Combusken, it will miss out on Double Kick (already missed) and Sky Uppercut. If we don't evolve to Blaziken by 36 (the first possible level) we will miss out on Blaze Kick. However, if we keep it as a Torchic forever, we learn Flamethrower in the early 40s, something neither Combusken nor Blaziken learn naturally, and a move which is better than Blaze Kick (since no physical/special split yet). So at this point IMO it's best to just stay as a Torchic forever, unless we can somehow coordinate evolving into a Blaziken at exactly 36.
No, because we'd never evolve it. Shroomish would still be helpful against Roxanne though. Our other options would be Ralts, Wingull, or Abra if we can find a way to level it up.