@jamie I would wait until a hot day and then repot that tree into a chunky, free-draining soil mixture and water generously using a heavily diluted water soluble fertilizer. You might also consider pruning off any dead or severely compacted roots during the repotting, as you really need healthy feeder roots in order to take up nutrients. Ficus tend to develop large bulbous roots if you don’t trim them, but the bulbous roots don’t really help with water/nutrient uptake.

Once you start to see the tree bounce back and put out new growth, you should be safe to trim those long branches back and encourage more dense branching.

For a chunky, free draining soil: I like using a combo of Fox Farms potting soil, reptile bark, medium or small sized pumice, and perlite. It’s not a 100% inorganic bonsai soil like the pros use, but I don’t have any trees old enough to warrant that treatment. Also, ficus are fast growing tropical trees that grow to monstrous size in the wild, so I think in general they do better with some organic material in the soil.