Bitcoin won't "die" just because it is unprofitable for some miners to mine. If the difficulty rises to the point where some  miners stop mining, then the difficulty will fall (because some miners stop mining). The result is an equilibrium where the value of bitcoin limits the difficulty. This point was reached in 2012 when GPU mining prevailed. It will happen again with ASIC mining.

The question of ability of small miners to mine depends on the cost of the equipment, the cost of mining and the difficulty. If the manufacturers can sell low-powered mining equipment at a price that allows small miners to profit, then they will. Sales of the USB miners showed that there is a very high demand for low-powered equipment, so I think that there will be manufacturers that will try to supply those miners.