Will it not kill bitcoin and make it useless?
Okay, let's assume that there is that "zero" transaction. Then the supply will be lesser that will make the demand higher. But in reality, this is a very impossible thing to happen. And miners will always be there, as a matter of fact there is no bitcoin user that isn't holding. Most of us have some bitcoins that are keeping, so it won't kill bitcoin.
No, the supply isn't there. Since all of us will hold, there's no movement and supply in the market. And we know on how the law of supply and demand goes on. But it's hard to think that there would be zero transaction for real and I guess the miners will not actually depend on the block rewards and confirmation of the transactions.