Recently, I was shooting in a remote area with no internet or cellular data coverage and had a vision sensor calibration error. Tried to connect to the laptop to do the calibration and was unable to get the software to run because I needed to login. Couldn't perform the calibration and was forced to use my P3P to finish the shoot. Does anyone know if there is a way to use the software while offline?

Yes you can use it offline. Just strat the Ass2 on the computer first, plug in the AC, turn on the AC and then ignore the log in screen and click on the CALIBRATION. Eitherway when I use Assi2 I always turn off my WIFI so it doesn't do anything behind the scene without me allowing it to do.

You can do a vision sensor calibration via DJI Assistant 2 offline. Just connect the Mavic Pro to the PC and power it on, click Mavic Pro icon on the upper left, choose Calibration.
We also have the tutorial about how to calibrate the Vision Positioning System for your reference: