The train is now stuck with 40 extra carriages, but there's no reason they can't just detach their former last carriage as they did before to cut away.
Melanie sees snow in the snow outside the train. When she tells Bennett about it, he replies that it is not possible because it is too cold. Temperatures outside the Snowpiercer are around minus 120 degrees Celsius, which means snow is possible. Experts say only at absolute zero would snow become impossible. Along with everything else. This claim about the impossibility of snow continues through series.