ive seen worse,but the long term effects are going to be bad.Youll slowly see dieback in the cnopy of the tree.Roots and the canopy are directly in cahoots with each other.After it starts to dieback youll prob have to deal with a heavy damage from insects attacking this stressed tree.1.WATER IT WHQEN IT IS DRY!The average tree needs one inch of rain water a day!A small shower will not cover this.It is a fairly young tree,probaly not over 80 years old.Dont know about anyone else but a 400 year old tree is rear around me.This is not one.2.Once those roots are gone,there gone!nothing else is going to grow in its place.youll probly start to see a large canker start to grow from the butt up.When this happens its time to consider taking the tree down.Armalaria root rot is one of the most common root rots of oaks and when you start to see this its bad new.3.When in dought, hire a lisenced arborist,your trees health depends on it!