If a small-ish group of people can buy the daily supply with a smallish amount of money, I would say that the system is in it's death throes.  1000 people spending $10/day could do so at 7200/day and a price of $1.40-ish.  So, I would say that we are uncomfortably close at this point and that interest would likely drain away.  Judging from the network activity, that seems to be occurring.

But it seems to me that it is also possible that rather than death, we could have some sort of a 'mothball' situation where current value holders put enough effort in to keep the system basically going.  If/when an obvious and significant need for such a solution appears, it could be that the existing Bitcoin solution is more viable than alternate newer solutions or variants of the Bitcoin solution.