Do PC-12 cells have to be stored in nitrogen?
The temperature at which nitrogen evaporates is about −195°C. Given the considerable difference in temperature between the current freezer and nitrogen vapor, I'm inclined to say probably not.

I suspect that it may be dependent on what exactly you are using the PC 12 cells for. Without knowing more detail about the situation, I would do my best to get ahold of some liquid nitrogen for your samples as soon as possible. When in doubt, it is always best to follow procedure.

Until you can acquire nitrogen, -80 is still far better than room temperature. Be sure to take note of the discrepancy in your notes and hope for the best.