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?
No, the only way there were no transactions is for bitcoin to be useless already since no one transacts with defunct coins, whether those are altcoins or fiat, so an scenario like that will never happen, just look at gold, most gold is stored and not much is done with it, but it has been around for thousands of years and it is still relevant.