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.
If you have just read the op's sentence he does say that all bitcoin users are holding its bitcoin and dont intend to make any transactions between among other users which means theres no activity.Supply is there but the demand is nothing then value would lessens or zero at all.