Well, if Lee got killed or wounded while in command of the AoNV in an 1862 Overland, then command would devolve onto the next most senior commander.
If Johnston had been removed from command for cause (wounded or otherwise) then it would probably be Huger or Magruder; otherwise, Johnston. (Of course, anyone could be appointed.)
If Grant got killed or wounded in an 1862 Overland, assuming Grant has been appointed as MG(R) and thus gained command of the AotP, the next ranking MG would take command. (Possibly McClellan, if McClellan is GiC; otherwise to some extent it depends on who is MG(V).)