So for the sake of argument, let's say I am the developer of this apartment. The market value of the apartment has now potentially fallen to somewhere between 345,600 and 400,000 ( difficult to gauge). But I have a binding contract with an individual who has multiple buy to let properties. If I pursue this individual I will either force him to complete at the original 500,000 plus price, or I will get a judgement against him for my costs, plus any damages I incur, including loss in the market value on the resale at a lower cost. And I know I can enforce that because I can get a judgement against him and worst case register it against his other properties and go for a well charging order forcing the sale of those other properties until I get my money.
The alternative is that I simply forfeit the deposit and don't pursue the rest of the money.
Difficult choice?