I don't know where you are but it is a bit early here to repot ficus. Yes, it will regrow leaves, just don't overwater. Willow leaf ficus usually do defoliate.
Ficuses are tough, it will probably grow new leaves, Don't let the soil go completely dry. I have mine in akadama and kyriu, and I water when I see some of the surface rocks starting to change to a "dry" color.
Mine drops it's leaves every year when I bring it in for the winter, just to be sassy. I freaked out the first year, now I'm used to it, they will come back.
Not that tough at all and many ficus like to get a bit dry. There are over 800 species and over a dozen easy for bonsai. Do not overwater a bare ficus, especially a willow leaf. The only one I ever killed was over watered when bare leafed.