What happens if all of the Mobile Hotspot data allotment is used up before it expires?

The hotspot usage will draw from the high-speed data allotments of your plan. If you have reached the the hotspot data allotment, then no further hotspot data is available. If you have reached your plan’s high speed data allotment, but have not reached your hotspot data allotment, hotspot is available at the plan’s current data speed.