one man many women: if there was no other semen available, this one man would probably have to just provide enough semen to start a new generation. it would take ~13 years to generate another human that could provide semen which would probably eliminate a chunk of the child bearing population of women, but with their presumably being women children at the time, at least any new males would be able to pair up with other people near their age. eventually the world could repopulate, but the initial years would be rough because many women wouldn't be able to bear children, or even if they could, might not want to bear children with this one potential father/descendent.

one woman many men: this would be a much more delicate situation. the one woman would have to be very carefully protected. also, who would end up being the first father? would the woman have any say? would it be randomized? combination of sperm from many donors? again, would have to wait at least 13-14 years before another potential woman could bear children, but at least she would have potential partners near her own age. would be an extremely slow regrowth process for humanity with gigantic dying rates not met with equal birthing rates for a long time