Genesis 6:
18 And I am establishing my covenant with you, and you must go into the ark, you, your sons, your wife, and your sons’ wives with you.
21 For your part, you are to collect and take with you every kind of food to eat, to serve as food for you and for the animals.
So there was only going to be food for the the animals and 'you' which, from V.18, means Noah and his family. No consideration was made for extra food for any who might repent.
There was never any hope for pre-flood mankind. It was a forgone conclusion that God would wipe them all out. Noah's preaching wasn't of hope - it was a judgment message.
When I was in the process of leaving an elder came round and tried to use the story of Noah and his preaching work to encourage me. When I pointed out about there only being enough foood for Noah and family he went very quiet!