I don't know, I think it made sense. The other people she told all had a good reason to believe her, Harrison because he knew Tru and trusted her, and also because he knew about what happened at her mom's funeral. Davis, obviously knew about her because he was saved by her mother. I think Luc was too grounded in the probable that he was blind to what was really possible, and having him continue working in the same building as her, still thinking she was either crazy or lying, would have slowly gotten to Tru.
His death also showd how far Jack was willing to go in his battle with Tru, and made the battle more personal for Tru, and a lot less abstract than "live vs. death" or "what is fate?".
Also, on a more technical note, how on earth would they bring him back? Lets look at the options:
-Ghost
-"It was all a dream"
-He asks for help (from 6 feet under?)
-Tru defeats Jack, thus raising him from the dead
Ultimately, it was Luc's lack of faith that led to the perminance of his death. She can rewind multiple times (like in the episode with the heart transplant), so the only possible things preventing him from asking her for help were either a) fate or b) he wouldn't let himself believe it was an option.
Also, his death may lead her to question why some corpse's ask for help, and why som don't, thus leading us into an entirely new storyline.
