Realistically, expect about 800 watt hours of real world usable power from your 1000 wh rated battery.
Range, as stated above, varies greatly with speed. At the worst end, ripping it 30 mph, you will get 35 to 45 watt hours per mile. But depending on the quality of your battery, you may get even less than 800 wh from it per charge. What happens when you draw hard on a lesser quality battery is the battery heats up, which wastes some of your power.
So at 30 mph, you might only get 17 miles out of it. But as said above, if you can run more like 25 wh/mile, then your battery is happier and stays cooler. 800 wh divided by 25 wh/mile is 32. 32 miles can be expected if you run 20 mph, and pedal with moderate effort.
You can do better still, by riding 15 mph, and pedaling with moderate effort. At 15 mph, your pedaling is now able to make up at least 25% of the energy used. 150 miles is not going to happen, but 40 miles is definitely possible from 800 wh of battery, when you ride 15 to 18 mph, and pedal with moderate effort.
To limp home on nearly nothing, just barely tickle the throttle. This tiny amount of power to the motor will eliminate the drag from the motor. Wont make the weight go away, but you at least don't have the motor dragging. You can use this to coast down a hill faster too.
You can make the weight go away too, with just a tiny, tiny bit more throttle if you need to. Just enough throttle to make the bike creep 5 mph or so. But really, what's the point of that except to limp home on a nearly dead battery? Then you could go 140 miles, but you still have to pedal just as much as if you rode a 15 pound bike 140 miles.
40 miles out of that size battery, is about the max that is worth it, letting you enjoy a ride longer than you can go on a normal bike, without pedaling hard at any time. When I was sick, pedaling hard even 5 min was impossible. Only the assist let me get out of the sick room.