If it poss. For mild to mod. Laryngeal nerve damage to heal after 3ys. With voice therapy? Do those techniques need to become a way of life forever?

Laryngeal Nerve. The cause of the laryngel nerve injury is important in trying to predict the chances for recovery but ulitmately, the potential for recovery is greatest in the first year and is unlikely at 3 years. The voice therapy techniques should be continued if you feel they are beneficial.
Yes and no. If the nerve isn't completely paralyzed or severed, then recovery is possible within a year. However after 1 year there will be no return of function. Voice therapy is used to strengthen the opposite cord so that it compensates for the weak one. Those techniques should be practiced until they become habitual. If voice therapy isn't successful then other procedures can be tried.