Could better Austro-Hungarian mobilization and Bulgarian intervention produce a 1916 peace that saves Imperial Russia?
Short answerNot as a single plausible divergence; the proposal changes too many independent decisions and still may not repair the wider strategic situation.
NotesThe suggested route combines corrected Austro-Hungarian mobilization, Bulgarian action, a 1916 peace, and Germany not sending Lenin. This is a bundle of major changes rather than one plausible divergence. Better execution by Austria-Hungary would not necessarily overcome the wider strategic mistakes and rigid assumptions shared across the belligerents. A counterfactual becomes less informative when every obstacle is removed by a separate intervention.