I think you underestimate demand massively. If bitcoin price ever starts to drop precipitously, it will be scooped up by a mass of buyers who have a ton of money to blow and a lot of interest in maintaining price. The only thing that could cause a real collapse to sub 4 digits is if something went wrong in the actual protocol or some unforeseen exploit occurred that affected the system in a way that was unrecoverable. If the cryptography and incentive systems continue to function, the price will probably never approach 4 digits again even if Tether blows up (which it probably will).