I hate to be the person saying something like "koalas are only in terrible trouble, not awful trouble", because it's clear that the issues are serious (not to mention the over-arching issue of climate change). But in an article linked from this one there's this quote:

"The number given by the Australian Koala Foundation is much lower than the most recent academic estimates, but experts agree that koala numbers in many places are in steep decline."

So the line about "experts" in the Forbes article are the Australian Koala Foundation, not academics who study koalas.

As I say, I'm reluctant to bring this up because it may sound like I'm deliberately trying to diminish the importance of habitat destruction on koalas, which is clearly serious. But the headline for me feels like Forbes chose the most emotive possible interpretation to gain some clicks, rather than it being a sober analysis of the (clearly serious) situation, and therefore I'm doubtful of the "functionally extinct" part of this.

The reason I'm quibbling is that if this claim is over-stated, it's going to lead to people thinking "well, last time they said functionally extinct it wasn't true, so it probably is this time," and will make these kinds of claims easier to dismiss in the future.