I accidentally killed bernard in the Copper Coronet. Now that Jahera is supposed to talk to Bernard what does he say to her and do I need to restart the game?

Why does Jaheria need to talk to Bernard? As I recall, the quests that relates to Jaheria do have dialogue with Bernard, but it is not a mandatory to talk to him in order to complete those quests.

No just follow the other clues in your journal to solve the quest.
Killing Bernard is bad for other reasons however, he's a merchant who had good stuff on him (like the crossbow of speed).