Most breeding loans work as follows:
If the snakes are of equal value you split the litter 50/50
If one snake is of higher value you split the litter 67/33.
If their is an odd number of offspring you give the odd one out to the person breeding the animals.
For a breeding loan to work you really have to trust each other. Otherwise one party feels like they are getting screwed. It is easier to setup a breeding loan with splitting offspring as that way if no offspring are produced you both get nothing.
As for your case above since you guys setting on a sum of money I was say that since the money was paid out and the person did get what they paid for (a breeder animal) I would say that the money should NOT be returned. A breeder animal was provided and as far as that animal goes he did his job (breed the females). If the females decided not to produce that is upto the females.