The Mishna (Sanhedrin 10) states that Dor Hamabul do not have a part in the world to come:
דּוֹר הַמַּבּוּל אֵין לָהֶם חֵלֶק לָעוֹלָם הַבָּא וְאֵין עוֹמְדִין בַּדִּין
The generation of the flood has no portion in the world to come
In my understanding, the punishment cleanses the sins, and the person is "free to continue". At least this is how it works for us, Jews.
On the other hand, G-d openly admits, that their sins stemmed from the evil inclination He initially implanted in all of them, so I suppose the punishment is sufficient.
Why don't they deserve a portion in the WTC?