Hello and thank you for your question.
Yes nerve block can be helpful to ease the pain from TN.
Before having the procedure his physician will provide him the information that he may have facial numbness for atleast 24 hours after the procedure so he may have difficulty in chewing in that 24 hrs.
No he would not likely have a facial droop and would expect the relief. If the physician uses glycerol as neurolytic agent compared to alcohol than he may have 100% good positive result.
The potential side effects, the most common of which is swelling and bruising of the face. Rarely, some residual weakness of muscles or difficulty in breathing or swallowing can occur as a consequence of the involvement of other nerves. If these side effects arise make sure his physician is aware.
Please get back to me if you have any further questions. Thank you.