There's no reason why they wouldn't switch to litecoin or some other scrypt coin. Many already have, and as it is currently more profitable even without too many ASICs, I think that's what will happen sooner rather than later.
I chose to sell off my GPUs this month (yes they're already sold) - I'm not interested in mining alt coins with GPU. Frankly 2+ years of that noise should be enough for anyone. I have not (as of yet) replaced any of my lost hash rate with overpriced and under performing (but instantly available) asic devices. I'm debating simply holding the bitcoin for awhile. I do have early orders with BFL for enough singles to not make the missing hash rate matter if bfl delivers this year. Until then (or something else becomes quick to get and has good power profile) I'll be fine with my reduced electric bill.
The only rule for buying mining hardware now is most mh/s/j wins.
We're just getting out of the 'bad old days' of bitcoin mining and I don't understand miners who are willing to put themselves through that again for an alt coin that's clearly inferior to bitcoin.