If you’re thinking about switching to Litecoin mining, do some research first, use the calculator such as this one for Litecoin https://www.litecoinpool.org/calc and this one for Bitcoin http://www.alloscomp.com/bitcoin/calculator, then do the comparison, what I normally do is a simple compare 100mh/s BTC = 100kh/s LTC, so if you plug these # in you will notice not much different. Until I see a big different then I would switch over to LTC mining.
What I’m afraid of is when BTC level rise so high, the LTC level will rise with it and mining indeed will never be sustainable, profitable, … thus all mining via GPUs fall off the network and even with ASIC rigs probably will not be able to sustain much either. So all these mining appears to be for short term, however if mining drop off the network I believe the level of difficulty will drop also, but will people drop off the network? I don’t think so, more rigs will be use to mine and mine, even real hard they will still do it LOL, some does it for fun, some want to make money, and some just do it to kill free electricity they get renting.