Theoretically, if it had taken the vampires less time to defeat them, then they'd have been able to kill them off before Durkon could convert his vampire, and Belkar wouldn't have been there to destroy him. Durkon would then have had to fight the other vampires on his own, and he might have lost (or the vampire spirit might have reestablished control). In that sense, losing closer might have made all the difference. Now, did Hilgya make the fight last longer than it would have otherwise? Hard to say (too many variables), but I'm leaning towards "yes".

But I'm not sure what this has to do with anything, to be honest. Yes, I do think she's just contributed to saving the world. No, I don't think that was her motivation.