Storing for the sake of savings and spending it in the future will never kill Bitcoin but hoarding it and not spending a single satoshi of it will definitely kill the currency. There is no transaction, liquidity and even not used to buy stuff, so merchant accepting it will definitely look for alternative. Bitcoin without transaction (trading, spending etc) is more likely a dead currency.
But it is doubtful we will reach the point where people hoard just for the sake of hoarding, those that are storing bitcoin do so because they want to obtain a profit from bitcoin, so if the price skyrockets then we will see many of the people that said they were going to hold bitcoin for decades selling their stashes in a matter of days.
I believe continuous rise in price and instability encourage people to hoard further for.
1.They expect more price hike in future hence more profit.That is why less sell order during bullish days.
2.Small investors fear they might not be able to buy back if they sell.
