The New Hampshire Bar Association Ethics Committee, in May 2007, wrote an opinion or (my term) "white paper" as part of its ethics studies on closing a law practice.

It’s a good summary of factors to consider, though certainly not complete.  And, since the date of this opinion/white paper, the Supreme Court of NH has approved a new set of Rules of Professional Conduct which include Rule 1.17 explicitly permitting the sale of a law practice in NH for the first time.