Yes, it is good news that a wolverine from Idaho found its way to the Sierras, but you have to temper that news with the sad fact that even a population of a hundred Sierra wolverines would be in a precarious situation in terms of long-term viability. Very small populations always live on the edge of extinction. There's no evidence this one can even find a mate.

Then again, even new volcanic islands eventually acquire diverse populations. How quickly they get populated depends on how close they are to mainlands or established islands.

The Sierra has similarities to an island, in that the wolverine had to cross some hostile territory to get there from Idaho. As long as there are wolverines in Idaho, there's a chance they'll re-establish in the Sierras.

A really great book on population ecology and extinction is Song of the Dodo by David Quammen. I highly recommend it to everyone.