Dear doggieR,
The owner have no case against you. This delay is cause by the seller and his agent. you can sue the agent and the seller. however it will be a very complicated case. have you check when is the mop date for the hdb you are buying. if you are really interested in getting the hdb flat, have you see the MP? ask them for help.
yes, i have hear of the common law. but i personally have not deal with such similar case before.
you can wait for the appeal or ask the them to refund all deposit and purchase other hdb flat.
if the mop is not met the otp is void. so deposit have to be refund.
all the best for ur case