What would go wrong if a cell did not replicate its DNA before beginning mintosis?

If a cell did not replicate its DNA (during the S-phase) before beginning mitosis, then the two identical daughter cells would only get one chromosome from each pair. This, instead of the normal (diploid) 2 pairs of each chromosome (2*23=46), would lead to two haploid cells with 23 total chromosomes each. They would be unable to function and sustain life, thus would likely die soon after division.