It's pretty late in the game, at best a Hail Mary pass for the end-zone. Repot it in whatever bonsai mix you can buy from a legitimate bonsai source, muy pronto and put it outdoors in full sun. Water every day such that it is never dry as a bone, but does go through the normal and healthy wet, dry, wet, dry cycles. Feed every week with Mircacle Grow. If it recovers with new growth you will have another challenge: how to acclimate it to indoors levels of light just when it needs all the growth it can get to survive winter. Normally, on or about September 1st you would begin the process of adapting it to low light levels by shifting from full sun of summer to part sun to dappled shade to full shade to a good window in the house over a period of 4 or 5 weeks, the longer, the better. This would avoid having all the leaves grown in full sun from falling off. You don't have that luxury. You will need to compress that schedule and towards the end, when it is under 50°F overnight, take the plant inside overnight and put it outdoors, in the proper light conditions of the process as above, until the daytime temperatures are under 50°F in the shade during the day. And finally, repeat after me. "Our Father, who art in heaven...