What Causes Changed Voice And Loss Of Body Balance While Treating Vestibular Schwannoma?

My father, 78 yrs old, was affected by vestibular schwannoma in his head. It was detected 1year and 7 months ago and quickly operated partially (due to chance of damaging of nerves) but worned by the surgeon that it will come back within next 5-7 years. Before operation we observed that his organs were getting weaker rapidly. Within 3 days he lost clear voice. After operation his condition was improved by 80% but one side ear and leg became weaker. Recently he is again saying that he has lost mostly of balance of body during standing and has to use a support. Is there any treatment to avoid firther operation?