1. Why did you mention in the MOU that the cash is for loan purposes? Insertion of this clause in MOU can actually prove that you took money from the buyer as a loan and you are liable to repay it with interest.
2. If the time for execution of sale deed has been mentioned in the MOU the buyer has to adhere to the same. It is incumbent on the buyer to obtain the loan approval prior to the expiry of the time for the execution of sale deed.
3. If the buyer fails to pay the balance amount within the time period for execution of sale deed then you may issue a legal notice for cancellation of MOU to him. The token amount is ordinarily forfeited, but this is subject to an agreement to the contrary.