Your question makes no sense and indicates that you have either confused Icelandair and Alaska Airlines, or simply don't understand how Frequent Flyer Programmes work.

(The original question also is worded in a way that indicates you may not understand how FFPs work. It's not so much whether Icelandair "belongs" to any FFPs - there is an FFP, called Saga Club, which itself belongs to Icelandair. As post number 5 shows, there are a limited number of other FFPs that may allow Icelandair flights to earn credit in those programmes - namely Alaska Airlines, Finnair, and Jet Blue).

The bilateral partnership between Alaska Airlines and Flying Blue - which is the focus of the quote of your most recent post - has absolutely nothing to do with Icelandair.

Icelandair and Flying Blue have absolutely no relationship. So the fact that Alaska Airlines and Flying Blue are parting ways has absolutely nothing to do with Icelandair.

(To avoid all doubt - flying on Icelandair will never earn Flying Blue miles; flying on the Flying Blue airlines will never earn Icelandair miles; you cannot spend Flying Blue miles on Icleandair; you cannot spend Icelandair miles on Flying blue)

As post number 4 above shows, you cannot "circumvent" the lack of a direct Icelandair/Flying Blue relationship by going via an intermediary (Alaska Airlines) which, for the next few weeks only, is a partner of both Flying Blue and Icelandair.

Any miles earned in Alaska Airline's programme - whether by flying on Alaska, on Icelandair, or on any other Alaska Airlines partner - can only be spent on AF/KL flights for as long as Alaska and FB are partners.