I found a bit of information about drying of the ich parasite:
Does Ich lay Dormant, or is Ich always Present?
Ich is NOT always present in an aquarium, despite many claims to the contrary which is sometimes used to cover up for poor quality stock.
I have conducted tests (and read others) where I killed off any Ich (if there was any depending on the control group) and then subjected the fish to many stressors that commonly bring on Ich such as sudden temperature drops with NO resulting Ich outbreaks.
It is important to note that the Ich protozoan cannot live outside water and if dried, its cell wall would collapse permanently destroying this single cell parasite so this point also makes migration of Ich from anything other than transport via infected fish or similar water transfer impossible. This also goes for marine Ich (Cryptocaryon) which I almost never had problems with in tanks where all fish were carefully added and there were no previous outbreaks.
Which I got from this site:
http://www.americanaquariumproducts....ch.html#myths2