When there was a fire on Mir, Nasa said "Small Fire Extinguished on Mir" [1], and the actual thing was pretty severe: "The flames were large enough to span the breadth of Kvant-1, cutting off access to one of two Soyuz escape capsules", "Thick smoke rapidly enveloped the entire station, forcing all crewmembers to don oxygen masks." [2]
Given all the recent trouble Roscosmos had with the new module in addition to the engine malfunction, I wonder how bad the situation really is. What's the worst that can happen here?