The Mishnah taught: If it died or broke (e.g. its leg and can no longer work), the owner must supply the renter with a replacement donkey.

R. Yochanan: This refers to when the renter said 'a donkey', but if he said 'this donkey', the owner can tell him, "You wanted this one - take what is yours!''

Rav Huna: The owner must sell the carcass wherever it died and must give the renter enough money to be able to continue his journey.

R. Zeira: If with the money from the carcass, the renter can afford to rent even a small donkey, he is not obligated to replace it; if he cannot, he is obligated to replace it.

R. Huna: If the value of the carcass is enough that he can buy another small donkey, he is not obligated to replace it; if not, he is obligated to replace it. (R. Huna is of the opinion that one should not consume the money of the owner. Therefore, it is better that he buys a donkey with the money rather than use it for a rental that will consume the money.)