You should easily last another weekend. You going to MSRH this weekend? That track is much easier on tires than TWS.
I ran my last set of NT-05's down into the wear bars and as rhouck said the grip goes away but I'm too cheap replace tires with tread remaining
. I also swapped my wheels left to right at their last event. There wasn't enough tread left to make a difference which direction the tire was rolling.