Board Thread:General Discussion/@comment-30160565-20170911010244/@comment-29602226-20170912182925

They would go insane with lust. They could survive getting their SE from other sources, but they couldn't reproduce, so most species would go extinct. The only ones who would be left would be the immortal ones (Undead, Magical Materials, Shoggoth, Atlach-Nachas, corrupted Angels and Elementals, maybe...), Zombie family ones born from corpses of dead mamonos, Ghost family ones born from the unsatisfied souls of deceased mamono, and monsterized Angels, Elementals, Fairies, plants and pets.

So, if they were left alone for like 10,000 or 20,000 years all that would be left would be Magical Materials, Undead, corrupted Angels, a few other immortal or extremely long-lived species, and the few Fairies, Angels, Elementals, plants, cats and dogs who got monsterized when attacked by mamonos...

If the mamonos were left alone for just 100 o 200 years, many more species would survive.

Anyways, upon re-encountering Humanity they would go into a rampage...

LoveCrush76 wrote: That would just be Monster Musume no Iru Nichijou.

The monstegirls in Monster Musume no Iru Nichijou were never fully isolated from Humanity. Harpies and Lamias would have gone extinct without human males, and Centaur culture have evolved in a way that they need the help of human men in order to have sex, even if Centaur males are the one actually inseminating the females...