This tree is most likely a goner. roots are simply too far gone and its too late in the season for much, if any growth. The growth you have is extremely weak and is a last gasp at survival.
From the look of the punky rotten wood, this tree has been stressed out for a very,very long time.
Also FWIW, If you're looking to help it recover, the soil you've got it in is far too fast-draining to help roots recover. The root crown is also exposed. Both of those things tend to make what roots there are dry out. Submerging the tree in a tub of water at this point won't help it much. New roots (Even on BC) tend to grow and regenerate much more quickly when they have some air circulation through the soil.
If this one were mine, I'd get a bag of regular potting soil, mix is half and half with your bonsai soil. Plant it in a deeper container, so the soil reaches at least three inches above the beginning of the root crown and then provide substantial winter protection.
I would avoid treating this as a tropical. You run the risk of pushing the tree too hard. Weak trees in constant warm humid conditions tend to develop fungal issues.
Ideally, I'd plant it out in the ground in a sunny spot for the fall and winter and make sure it's protected from wind. I'd bury the root crown and leave room at the bottom of hole for some gravel to be mixed in with the dirt. Let it be until next spring. See what happens.