First of all I don't think people are going to stop using Bitcoin , because it's the future and who doesn't want to be a part of the digital currency.
The decrease in people using Bitcoin would eventually lead to the rise or a much stable condition than it is right now.
But if you are saying that the drop in usage is huge then it might be a different case , Because no one is there to exchange them which will lead to drop in price.
People will lose faith in Bitcoin and the time might come when it's worth nothing.