I would plane 3/16" from the back, and add a 3/16" thick maple/ash backing. Why? because maple/ash should be a better backing for hickory than hickory itself, and I would like to proove it.
some arguments;
- hickory is an incredible tension strong wood
- hickory bows often get quite a bit of set; the back overpowers the belly
- because hickory seldom crysals, it should also be very compression strong,, but just not strong enough to cope with the tensile strengths.
a softer (maple/ash) backing wouldn't overpower the hickory, resulting in less set. Both maple and ash are lighter woods than hickory, so there's also a weight advantage. Less set, less weight results in a faster bow.
a damaged bow is a nice thing for experiments.
but; maybe you can trap your bow, getting rid of the damaged area, and getting rid of some weight. A nice temper will take the set out of your bow, changing it for a nice reflex. The now trapped back won't overpower the belly. this results n less set, less weight, and more speed.
you can also plane it down, temper it, then add the maple backing. It's all up to you.
Nick