His FC record, unlike the Don's, merely great and not inhuman. He averages in the mid fifties in FC cricket and I'd look for his Test average to come down to around that point by the time he retires.
If he really was that great, he would have scored more in FC cricket. The Don averaged almost the same in FC cricket as he did in Test, showing it was more than a 'patch' he was going through. The Don had 28,000 FC runs in 234 matches at an average of 95 with 117 centuries. So we know his talent level wasn't overly exaggerated in Test cricket through luck or a purple patch.
Hussey is great in FC cricket (195 matches, average of 54), but he is nowhere near Bradmanesque and is really closer to most of the merely 'very good' batsmen of this era. Obviously, if his average is 90 after a decade of international cricket - then obviously his FC record is a moot point. I think a good reference point is found in his ODI average. After 32 ODIs, it was over a hundred, after 50 ODIs it was under 75, and now it is below 60. Something similar will happen in Test cricket, but depending on how long he sticks around, he may still end up with an average of 60+.