OK, checked with a Spirited source this morning and Avatarland isn't dead ... yet. It seems to be a matter of when, not if.
Disney and Cameron have a distinct difference of opinion over how this should be done and, more importantly, how much it should cost. And because of the strange new world the movie showcases, turning this into a theme park world that isn't all screens (something Cameron put his foot down early as WDI did want a second generation Soarin where you flew on one of those dragon-creatures over and through and around Pandora as the highlight E-Ticket experience of the land) has proven very problematic.
Disney is also aware the general public (not simply crazy Disney fans who post on sites like this) gave a collective yawn to the announcement AND the two new films are behind schedule by quite a bit and knowing the perfectionist that Cameron is may be delayed by quite a while, giving Disney nothing in the pop culture of the times to play off of when the imaginary land opens.
I was told if they take this off life support to not expect any announcement 'if they can help it' ... that it will quietly be taken off the slate of working projects and hopefully no one will ask any questions.
So, I guess you can say it isn't dead ... but it's like a dying hanging upside down tree that no one is nurturing at this point ... and that fanbois want to see cut down so they can get a better view of Wishes and a fiberglass castle!
~Too much snark there?~
I've been out of the loop a bit but I have seen a hint or two that seems to support this today. Trial balloons seem to be going down faster than logs on Splash Mountain. I wouldn't expect anything to magically show up to replace it anytime soon if the plug gets pulled. Burnt a lot of resources in trying to get it off the ground and it will take a while to reset and redirect.