Yes, mtDNA will carry over with most "genomic DNA" isolation kits. It represents a small fraction (between 1-5% depending on cell type) of the total DNA extracted but can be detected by PCR. If you are using mouse cells you can use the following primers with PCR;
@ Michael Ian Robson, I did not know mitochondrial DNA was 1-5 % in genomic DNA extracts. Can I have a reference for that percentage ? I am not asking to "google it for me", but in case you have the source, I would appreciate it very much.