Is it truly impossible for the PG to seek a separate peace? The Czar's government made the promises to go to war and failed in gaining victory. If his supporters persist just release he files concerning involvement in the assassination, corruption, incompetence, the threat alone should quiet much dissent. Germany essentially only holds Poland and they are not a critical territory or minority to fight for, in truth they are a poison pill to give. A-H is likely very willing and would pressure Germany. Germany needs raw materials and food, exporting food would begin the restoration of normal commerce. Shoot Lenin if he arrives, arrest Trotsky, no revolution. If it is before the USA has committed to joining it can be presumed Germany wins so who cares what the British or French think? Blame the Czar, peace with honor was salable, it is easier to ask your allies why they failed to get Germany off your back break through in the West, open the Straights, etc. It may be implausible for the actors involved but was it that impossible?