Not really, the equilibrium will be influenced by the profitability certainly enough but I doubt we'll see mining become truly UNprofitable.

I have rigs in my living room, bedroom and kitchen. They make a ton of noise, lots of heat, I've had to add portable air conditioners to parts of my house, I have to keep one eye on my pools' status tables to make sure they're all still running and connected, every so often they need reboots, maintenance, etc. It's not the worst job I've ever had but it's still a bit of a hassle and there IS a baseline income below which it's no longer worth my time - and that baseline is > $0.

If you were correct, people would only leave when the net gain of running a miner became zero, which simply isn't true. Once we fall below a certain level of profitability, we'll begin to cross other folks' (and maybe my own) personal thresholds and they will pack up their rigs and go home. At this point, difficulty drops and mining becomes more profitable again.

Check out this post: http://forum.bitcoin.org/?topic=7427.0

There's a wonderful chart there that shows an arbitrarily scaled price over difficulty. See how it dips then climbs and repeats that pattern over and over? It's called homeostasis - you may have learned about it in your Biology class, but they should've taught it in Economics as well