If it's just an ice age on a planet well inside their star's conservative circumstellar habitable zone, then moving with the cold would work albeit with the risky loss of infrastructure and knowledge given their reduced numbers. On the other hand if it's a world right at the edge or even beyond it which only worked due to a long period of volcanism and/or early solar activity, unstable dynamo or the like, then they might be heading for iceball. In that case yeah, it's nonsurvivable without at least a high enough tech base to move to semi-closed environments with synthetic power sources, and if they're not on that path already it's probably too late. Of course they could be on a metal poor world and be screwed out of even that chance too anyway.