It's not the last generation. There have been one or two generations after their disappearance, The Queen's father or grandfather was the last king I think, I don't quite remember. There seems to be a ritual or some other way to make babies but we don't know what exactly.I found it pretty weird how chill everybody is about almost all of the men being gone. Like "whelp, we're the last generation, might as well carry on like nothing has happened."
From that plot point alone I was expecting all of the young ladies to be absolutely baby crazy and jumping on your dick all over town, but nope, they don't seem to care about saving the human race in the least.