Solely? Authors who write for a living write lots of books, not rely on one.

There are many ways that such scholars can get paid. For example, they may get hired to be professors and teach it in a college. They may be hired to authenticate alleged Dylan memorabilia. They may get hired as expert witnesses in a legal dispute over it. They may get hired as appraisers when auctioning/insuring the stuff. They may get hired by museums to curate, organize, and present a display of Dylan stuff. Etc.