Shutting down the GPU farms will be gradual as different countries have different electricity rates, the difference in electricity rate can be 10x between to countries.
CPU mining fizzled out this same way. Eventually even the bot owners (who stole the compute time + electricity from their marks) quit even though it was still technically profitable because even the small effort put in yielded so little value in return.
GPUs are not returning great profit but still today decently profitable for the typical (paying $0.15 per kWh). But back a few months ago the prognosis was that "in a few months" it's all over for GPUs. Well, the ASICs took longer to start shipping in quantity but they are today shipping and this is what is happening without the backorders even coming close to having been cleared:
- http://bitcoin.sipa.be/speed-lin.png
Major movement in BTC/USD price can make things completely different, GPU mining can end next week if there is a huge crash in BTC price, or it can continue through this year if BTC gains value rapidly.
Nope ... an exchange rate rise, even hitting BTC/USD of $500 won't keep the pace anywhere near the difficulty rise. Start planning some other use for your GPUs.