Miners seem to all into several groups:

The hobbiests who are dong it with under 30 GH just for fun and are using USB stick eruptors.
Those guys really do not seem to care about ROI and just want to be part of the fun.

Then there are guys with 30 to 100 GH. They want to make some money but perhaps, could not afford or could not get bigger rigs.

Then, there are the guys who have more than 100 GH running. That group then can be divided into the guys who have a TG or more, the guys who got their equipment at a good price and the ones who simply bought a fast piece of hardware. 

I have ignored the guys who are mining on FPGAs and older equipment. Those guys probably paid off their initial hardware costs.

As the cost of mining goes up, the hobbiest and big guys will stay in. It is the guys in the middle, I imagine, who will be squeezed out. But, as they get squeezed out, difficulty might go down. So then more guys will come in.  But, if the TG guys come in, then the leaving of a few in the middle won't matter. I think it will force the arms race to be more intense until someone works on the lowest power at the highest speed and somewhere there is a point of diminishing return.