Yes, I would bring the fans back and finish today. I'm willing to bet less than one percent of the fans in attendance were satisfied with the race being called last night. Most would have been back today, and for those who couldn't, what does it matter? What does it change for them? Absolutely nothing.
And no, you absolutely do not need a specific "cutoff" as you said, regarding the remaining laps. It's a judgment call on a case by case basis, since there are wayyyyyyy too many variables. Again, context is everything.