Those who have gridseed units (and didn't pay stupidly much for it) will be able to survive a much larger profitability drop before reaching a point where they have to shut down.
Except, of course, when the new ASIC farms come online in the next 3-6 months, and everyone switches away to nScrypt and other algorithms which these ASICs can't handle.
At the moment the ROI for a Gridseed is in the 9-12 month range (accounting for difficulty), and I have little faith that straight Scrypt based coins will remain profitable for that long.
I think GPU mining will remain the best long term bet for quite some time now.
My point is not about ROI about rather about running cost.
These gridseeds have a very low cost to keep running, which means they'll continue to account for a large amount of the network for scrypt coins, even while profitability continues to drop.
And yes, my point is GPUs will either shut down or switch, thus leaving ASICs as only viable scrypt miners.
While ROI is relevant for the purchase of new units, it is not for the large amount of existing units already out there.
Existing units will keep running until the profit drops below the cost of running them.
But I already addressed all of that in my earlier post.