You know how when water gets inbetween cracks in the sidewalk and freezes, it makes the cracks bigger? Frozen water can break rock, let alone composite woods that are already "pieces". It depends upon just how much water may have gotten into the wood before it froze, but if freezing water can break rocks open, it'll make mincemeat out of wood composites. It's why they use them on internal structures that aren't likely to get wet to begin with.

The steel I-beam should hold out just fine. The composite joists I wouldn't be so sure of, nor would I rely on them later (call me paranoid, I'm an engineer. Safety factors are a big deal).

At the very least, renovations are going to be more than mandatory, plus a mold specialist come springtime (if the building isn't warm, then it won't be an issue. Yet).