If everyone keeps their bitcoin on hold then there will be no ups and downs in bitcoin market and it's price will drop from stable stage to bottom line. By such activity miner will also quit mining and there would be no more bitcoin mining system and it's quantity will become fixed at some million quantity. And all bitcoin accepting site will also remove the payment api and lot more chances to happen.
Wrong. If really no one spends their Bitcoin, it's price in fiat valuation can't drop to zero ("bottom line"). Instead it's market price will be frozen at the valuation the last time it was bought/sold. In fact the bids to buy Bitcoin may also increase significantly, because there's not sufficient supply to satisfy demand.
Ok, I was a bit joking here. Of course, if really nobody spends their Bitcoin it would be bad, because the currency would be in lockup state and have no utility. However such a scenario is entirely unrealistic. Even if Bitcoin would be dying there will likely be a huge selloff / constant decline in economic activity. Every sane individual who expects Bitcoin to fail would try to sell his/her stash before it becomes worthless.
ya.ya.yo!