Look at this just like you would the batter's boxes when the lines have been wiped out. At that point, it's left up to your judgment to decide "is the pitcher making contact with the plate?" If the plate were visible, you'd only call it if you were absolutely certain she's off the plate, right? Well, since the plate's not visible, you're just going to have to be reasonable.
Just because you can't see the plate doesn't mean it's not there. However, you'd better be damn certain she's off that plate if you're going to call it. Otherwise, you're in for a sh1tstorm from the DC, and rightfully so.