Mathilde is the one who negotiated with the Dolgan. Not having her there at contact makes an already uncertain deal even worse.[X] Write-in: Take Borek, Asarnil and Deathfang, the half the cavalry, and Lillijana to scout out the situation at Dum while the steam wagons continue to Dolgan territory with the Wizards and half the cavalry to pick up supplies.
The expedition picks up an infusion of food and assuming it takes one week for the steam-wagons to reach the Dolgan a round trip to Karag Dum (composed of 3 days there, ~1 day looking, ~3 days back) should rendezvous in time to tell them whether to continue or turn back. Leaving half the cavalry so the steam-wagons are a bit more guarded.
Whether the Dolgan are hostile will depend to a significant degree on how vulnerable the wagons look. Having only half the cavalry and no dragon makes them a far more tempting target.
The wagons are about to go off-road. This is the stretch of the journey where Rite Of Way is most needed. Especially after the head engineer died.