It is unlikely that you will damage your instrument beyond repair if you maintain and care for your instrument as each of our teacher's demonstrate in the video lessons in the chapter entitled "Getting To Know Your Instrument".
If you do happen to damage your instrument beyond repair or lose it altogether, you will be responsible for the total cost of the instrument minus the monthly payments you have already completed. You can either pay the remaining balance outright or continue to pay the monthly rental fee until the total cost of the instrument has been covered.