As long as there is no litigation, I see no requirement to withdraw as counsel.
Whether it is prudent to do so depends on the facts, including why the other
lawyer left and how close you are to settlement.
Mediation might be the way to go. This would provide an alternative structure
for settlement. Otherwise, it is the standard situation of dealing with an
unrepresented party. Which for me, means all contact with the unprecedented
party is in writing. No "3-way" meetings.
Honey Hastings
honeyhastings@xxxxxxxxxxxxx
office/Wilton NH 603.654.5000