The environment that has changed and the frequency of the p allele has gone down means that the frequency of q allele would go up, because the two frequencies are inversely proportional and their sum is constant.
According to Hardy Weinberg Principle, the gene or allele frequencies in a population will remain stable from generation to generation until acted on by an outside force.
Allele frequencies in a population will not change from generation to generation, as far as factors of evolution such as natural selection, mutation, and migration are not taking place.
