5- As far as the discussion of Nignaz. I think it is silly to make believe that Reb Chaim never claimed that the chilazon is nignaz etc. and it is only hearsay. I honestly believe that that is what he holds. But like every area of Halacha, not all poskim have to agree to one opinion. Besides Moreinu Harav Chaim, the rest of the poskim who discussed techeiles didn’t raise the issue of nignaz.
Obviously, this doesn’t mean you can’t be somech on Reb Chaim, but again it also means that it is not a black and white case.
In the times of the Radziner Rebbe, The Maharsha”m, Reb Itzele Ponvitzer, Reb Chaim Ozer Grodzintsky and other gedolei hador (including the letter from the Beis Halevi that the Radziner quotes) all held it was possible for techeiles to return, and obviously thought that Nignaz is not a kasha.
The Yeshuas Malko was misquoted as holding that nignaz meanas literally. Fakenews.
He wrote a teshuva explaining that the Radziner’s techeiles is based on assumption and not on rayos, and he writes:
איברא שאם היה נמצא תכלת בבירור והיה ידוע לנו כיצד צובעין, ודאי היה ראוי לאחוז במצווה זו אלא שאין לנו בירור גמור שזה התכלת
Doesn’t sound like he understood nignaz to mean that it can’t come back.
A few commenters quoted Rishonim saying Nignaz means you can’t find it. This isn’t true. Not one Rishon discusses if you can find it or not. There is however a rayo from the Ri”f that brings all of hilchos techeiles, that he obviously held that the laws still applied bizman hazeh, even though he doen’t bring the laws of kodshim.
For a full list of mareh mekomos on the issue see the article on the techeiles.org site from Reb Yisrael Barkin <<http://bit.ly/UA2er2>>