In other words, the question is "Was the February Revolution unavoidable"?
Realistically, with Russia's entry into the First World War there are two ways to avoid revolution; either check Central Power advances or keep the supply lines open through the Dardanelles with Turkish neutrality or a successful Allied Gallipoli campaign.
It was poor military leadership and a lack of food that caused the Petrograd workers to riot. Russia could remain on the defensive militarily, buying time for space if the Black Sea supply line remains open to Allied shipping. German/Austrian forces would encounter stiffer resistance causing more casualties and pinning down more troops. The Western Front might be eased resulting in greater Allied success.
So I would say 1915 was the crucial year for Russia. 1916 at a push - if the Battle of the Somme wasn't such an unmitigated disaster for the Allies and causes more troops to be transferred to the West.