So... RIA Novosti (Russian media agency) made a video, where they show the Russians ostensibly undocking the Zarya module and the US part of the station falls into the atmosphere (someone was playing with Kerbal Space Program since the US part wouldn't fall immediately as it does in the video). It's unlikely that the Russians on the ISS would endanger their own lives like this, but we live in strange times.
Obviously bad things would happen eventually, but what would happen in the short-term? Would the US crew immediately have to abandon their part? Could any sort of fix be applied?