You are thinking of 'Good Samaritan' law, which compels people to take action to help injured or endangered others. Here, because of the time issue, you are free from legal prosecution: in the Germany of the 1700's, when and where the literary story of 'Frankenstein' occurred, there were no such laws.

If these events had happened after 2009, though, you would be liable for up to a year in prison for failing to render assistance to any person (specifically) in your view that had been injured by the creature - and possibly for failing to raise the alarm to warn the town (though that charge would be unlikely to stick). If you stayed in the university, and saw no person injured, though, you could not be convicted. The law only applies to what you could actually witness.

But, within the given time period of the novel - or even the movie version - no such legal compulsion existed yet, which makes you unprosecutable.

Additionally, there is the issue of the 'Bystander Effect', which is a known psychological phenomena where people fail to take action because they are shocked or stunned into immobility. You could, as a last resort, argue this stance, and that because of the overwhelming horror of the event, you can not be held liable for inaction.

So, yes, sufficiently terrible circumstances do, in fact, paralyze people sometimes, and the law can be forced to account for this effect. The animation of a corpse against all natural law definitely falls under the category of 'sufficiently terrible'.