I can't tell what is informing the idea that people would lose interest in bitcoin and consequently, it would become worthless! All that really makes no sense, because the likelihood of such situation seeing the light of the day is very very slim. Simple Economics, simply dictates that, whenever anything - a car, food,asset, even water, etc, just about anything that is worth something becomes scarce and for whatever reason, the price of that thing have no option than to rise. That is exactly what lies ahead of bitcoin. It is limited in supply by nature, it has some enviable value attached to it and so whensoever it becomes scarce, those who have some piece of it should be ready to smile to their banks.
It might not work the way you think it will.
If some shit is scarce, that alone doesn't make it valuable. In the first place it should have some utility, and only then the scarceness of it will kick in determining its price. For example, air has an absolutely vital utility because we can't live without it, but it is not priced for the simple reason that air is not a limited resource. Bitcoin has utility, in fact, quite a lot of various utilities, but if it loses them in some obscure manner for whatever reason, its scarceness as well as limited supply will be irrelevant.
We are in the same boat, but it was you who misconstrued my post. Whenever anything with some value attached becomes scarce, it price is sure to go up. Bitcoin is endowed with some inalienable values, like its unprecedented low cost of transaction, a true global payment/settlement system, anonymity and above all free from the control of government. With all those qualities, it would take everything and yet people won't be dissuaded from spending or accepting this coin.