I apologize for my tardy response Hiflier. I have been thinking about how I might answer your questions (and whether or not I could).
1st a disclaimer: I was educated as a paleobiologist. I have studied fossil invertebrate populations with regard to their specific variations (variations within a species due to ontogeny - that is growth from infant to adolescent to adult), parasitism by competing organisms, and evolutionary considerations as they impact our understanding of the genus, family, and order classifications in a particular class of invertebrates. I have taken graduate level courses in genetics and evolution (but a long time ago - invertebrate zoology was one of my two minor subjects), BUT I AM NOT A GENETICIST!
So take what I might say with some healthy skepticism - and I welcome discussion from real geneticists (and I am guessing from your questions that you already know most, if not all, of what I am going to say).
Some good news: With regard to DNA, hair is amazingly stable in a variety of environments that would be considered risky in other respects. That is mainly due to the presence of cuticle, the outermost hard layer of a three-layered hair shaft (inner medulla, medial cortex, outer cuticle). The cuticle protects the medulla, and the medulla contains a lot of mitochondrial DNA (mtDNA).
Some bad news: Nuclear DNA (nDNA or nuDNA) is lost in the process of cornification - in which protein cells become hair. Although many people think that a follicle needs to be attached to a hair shaft for extraction of nDNA, nDNA has occasionally been extracted from the medulla of a hair shaft - sometimes months or even years after the hair has been pulled/shed from a human body - I guess this should be included under the "good news". In most cases the best that one can expect from hair in terms of DNA is mtDNA. mtDNA is not pertinent for ID'ing individuals, but works for ID'ing species (if that species' genome is included in an existing gene bank - and it should be useful as a match for higher classifications as well, such as genus, subfamily, and family). According to at least two hair experts, Sasquatch hair commonly lacks a medulla, and, when present, the Sasquatch medulla is discontinuous and not prominent.
A number of mtDNA studies of purported Sasquatch hair have suggested Homo sapiens, and the natural conclusion is human contamination. There are a variety of methods for decontaminating DNA samples, and actually hair, again because of the protective cuticle, is especially prone to successful decontamination. As I have said in other threads, there exist in all know human DNA (ALL HUMAN DNA) genetic markers that are unique to Homo sapiens, so any DNA researcher looking to verify human contamination or to suggest the existence of other than human DNA, must look for one, or a few, of those markers, else he/she is falling short of performing adequate study (trying to be kind here to past researchers - I would rather say #*&@&%$*!).
I think study of suspected Sasquatch hair is worth study, without regard to external environmental challenges and without regard to time in environment. I am not like the body of posters on this site (mainly inductive reasoners - some brilliant, some notsomuch) that can run through a myriad of explanations and possibilities addressing a single data point. I am admittedly not brilliant - I am a plodder. I try to gather a lot of data and methodically work through that data to try to understand it (that's a tough thing in this Sasquatch world containing a fair bit of purely anecdotal data). If I were confronted with testing old hair for DNA or making the determination no to do so because conclusive results might be unlikely, I would say do the analysis - one never knows what might turn up (my experience has been the more one learns, the more one realizes there is more to learn).
I had planned to address your questions more directly, but I am running out of gas. The subject does interest me, however, and I look forward to more communication with you.