Simple question, couldn't find an answer with search.

When attacking, my Barghest rolled a single sword, a morale, and a heroic result. Does using the heroic result to Howl (inducing panic) change the morale to a damage THIS turn, or do all results apply simultaneously, creating a damage, a retreat, and panicking the unit for future attacks?

You've misunderstood what panic does. You would NOT do additional damage this turn. The panicked unit has to count all of its own rolled flags as damage to itself. So it makes the target hurt itself possibly in the future. Panic does no immediate damage.