either of these options would be feasable and legal with the rules. Having a chainsword or not does not affect the model at all, if he does not have a second weapon to go with it. I am not sure that there is a writen rule but it use to appear that all units are assumed to have some close combat weapon be it a chainsword, knife, teeth, tentacle, spork, or vulcan nerve pinch.
Simple answer if you want to model it with a sword go for it, if not, thats fine too. Both are correct, WYSIWYG, and identical models in the rules.
EDIT:Ninja'd by Raktra