By not using the disguise you lost a bunch of potential experience points - but in the long run not important at all. There were a bunch of quests that you needed to speak to people to get, and to receive rewards for. No quest reward objects of any importance (the best reward the guy dropped when you killed him anyway).
You also missed out on trainers for certain skills, but again, unimportant in the long run. You can pay a bit more and learn the skills in the Battlefields if you need to.
No impact whatever on the overall plot.
