Can two denatured DNA strands reassociate?
Yes, heating the DNA above 94°C for some length of time will melt, or denature, dsDNA into two ssDNA strands. Upon cooling, the complementary strands will come back to anneal. The degree and completeness of annealing, or association, is dependent on a number of factors including the rate of cooling and structural properties of the DNA itself (%GC content, secondary structure). I would not expect that the majority of ssDNA strands will completely anneal to a single, complementary dsDNA strand. What is more likely is that the DNA mix will look more like spaghetti with one strand partly annealed to two other strands. When performing PCR, the primers are designed to be specific, and added in excess, so that you bias the odds of annealing to favour a primer:ssDNA association. If this weren't the case, we could not possibly have efficient PCR amplification.