Get paid after retiring from the real estate business

[Jamini]

My father has been a real estate broker for all his life. In all these years he has earned himself a good reputation and goodwill of a huge client base. As he nears retiring age, he does not want to give up his work for fear of no income. Is there any way out by which he can use his goodwill in the trade to continue earning without being actively involved in the business?