If everyone start storing bitcoin and there is no single transaction for days,all miners will quite mining as without transaction there would be no reward.
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.