This clause sets out in some detail all the various rights and obligations when a purchaser cannot meet the terms of the contract. It is very risky to sign an unconditional contract when there are matters that have not been properly addressed, given the risks of losing the deposit or even being sued for losses suffered if the property cannot be re-sold at the same price.
Seek the advice of a lawyer or conveyancer before signing an unconditional contract to ensure that you understand all the risks associated with the failure to complete a contract.