Yea, if all the transactions will stop then the interest on bitcoin will decrease and it will be in a great danger. But it will not happen ever. People invest here to profit. When they need the something like their necessaries they might sell them. Keeping one’s all money in bitcoin is not possible. None keep their all money to bank. They use it, pick that,use that, and again keep that. People will use bitcoin till it exist. Buying and selling will continue till it is alive.