Actually we must have to consider this fact as logical statement if no one spends bitcoin.
Actually this cannot be happen. Because in market if no one going to sale bitcoin and if demand is increasing then price of bitcoin can reach to sky.
But this will never happen. Because till date bitcoin mining is going on and till 2145 mining will be continued. So till 2145 miner only get rewards for verifying transactions made within network. In no one spend bitcoin no miner will get paid.
If nobody spends bitcoin, it is useless and therefore worthless.
Exactly, in that case Bitcoin would be worthless but this just can't happen. What should happen and how could anyone stop people from using it, not in this phase when Bitcoin is so much accepted and so much used. But like any other thing, if no one needs it and no one uses is then it's worth nothing.