Would you still mine bitcoin if the price went under $50 and difficulty stayed the same?
Assuming a consistent difficulty, 1GH/s would mine roughly
BTC0.00000052 per hour, which translates into $0.000026 at $50 per BTC. So unless you're paying less than that in energy costs per hour, you're going to find that mining is extremely unprofitable.
Obviously this would mean that just about every current mining conglomerate would close up shop until the difficulty dropped substantially or until the price per coin increased. But to answer your question, yes, I would continue to mine (at least for a little bit). Someone's going to have to find the 2016 blocks before the difficulty is recalculated, so I might as well take part