I read an article before that stated Ron Dennis actually wanted to hire Magnussen and that other young kid (can't recall his name), but it is Honda that insisted they should keep Button and get Alonso to attract more sponsors.
Ron wanted McLaren to have 2 young talented drivers rather than having 2 old, despite proven, drivers.
I cannot see Honda being big on Alonso. He just does not seem to fit in with their whole ideology. Button sure as he has history with them. If it was a move to attract sponsorship, then the team in particular and the sport in general is in a bigger mess than anybody thinks. Much as I am an Alonso enthusiast and would like to see him contend for another WDC, reality again arises and his "best before" date rapidly approaches. The younger-faster crowd is pushing in from the bottom and the seasoned crowd at the top all have better rides and career management.
Fredo is looking like taking that fishing trip on Lake Tahoe