Indian Department duties were divided between Alexander Cameron and Thomas Browne, according to His Majesty's Southern Department Of Loyal Indian Allies website:
"The first step was to find a replacement for John Stuart." "Both General Prevost and Governor Tonyn highly recommended Thomas Brown. General Clinton, on April 29, temporarily appointed Alexander Cameron to replace Stuart."
"In London, Lord Germain made a decision to split the Southern Department into two districts and give Brown the eastern and Cameron the western."
"....on December 31, 1779 the confusion and chaos in Indian Department Leadership came to an end."
Henry Clinton's Papers at the Clements Library at the University Of Michigan included the following:
Volume 57 April 30, 1779-May 11, 1779
Death of John Stuart, Superintendant of Indian Affairs in Southern
Appointment of Alexander Cameron as Superintendant of Indian
Affairs in Southern Provinces